This is not my work, it’s a copy-paste of the accepted answer to this question: https://superuser.com/questions/1023765/how-to-delete-the-recovery-partition-in-windows-10

The reason it’s copied here is because this is not just useful for people who need to convert a basic disk to dynamic like the question mentions, but also extremely useful if you need to expand your C: drive.

Note that this answer does delete the Recovery partition, but then it replaces that with a Recovery environment hosted directly on the C: drive. Why doesn’t the Windows installation process do this by default? It would make life so much simpler for people who upgrade their disks, or who run virtual machines with Windows on. It would also lead to fewer people downloading a certain very popular “Partition Wizard” that apparently bundles Avast in its installer.

Disable Recovery Agent Environment

First, you should check if the recovery agent is using this drive as the recovery environment. You can check this by running reagentc /info from an Administrator Command Prompt:

C:\Windows\System32>reagentc /info
Windows Recovery Environment (Windows RE) and system reset configuration
Information:

    Windows RE status:         Enabled
    Windows RE location:       \\?\GLOBALROOT\device\harddisk0\partition4\Recovery\WindowsRE
    Boot Configuration Data (BCD) identifier: 815b3db0-d49c-11ed-be7f-00155d019403
    Recovery image location:
    Recovery image index:      0
    Custom image location:
    Custom image index:        0

REAGENTC.EXE: Operation Successful.

The above output indicates that Recovery Agent is configured to use that partition. In the above output, note that harddisk0 (indicating disk 0) and partition4 (indicating partition 4). This should correlate to information you will use in the later diskpart commands. To disable Recovery Agent on this partition, run reagentc /disable in an Administrator Command Prompt:

C:\Windows\System32>reagentc /disable
REAGENTC.EXE: Operation Successful.

Now verify that the partition is no longer in use by Recovery Agent by again running reagentc /info in an Administrator Command Prompt:

C:\Windows\System32>reagentc /info
Windows Recovery Environment (Windows RE) and system reset configuration
Information:

    Windows RE status:         Disabled
    Windows RE location:
    Boot Configuration Data (BCD) identifier: 00000000-0000-0000-0000-000000000000
    Recovery image location:
    Recovery image index:      0
    Custom image location:
    Custom image index:        0

REAGENTC.EXE: Operation Successful.

The above output indicates that the Recovery Agent is disabled. Notice specifically that there is no indication of a partition being used. Now the Recovery partition no longer serves a purpose, so it can be removed using diskpart. Launch diskpart in an Administrator Command Prompt:

Force Delete Partition With DiskPart

C:\Windows\System32>diskpart

Microsoft DiskPart version 10.0.22621.1

Copyright (C) Microsoft Corporation.
On computer: DCX-VPN-ANYDESK

List the disks in diskpart. Look for the disk number referred to by the earlier reagentc /info command. In our example, this was disk 0. Use the list disk command:

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online           64 GB  1024 KB        *

Use select disk «disk number» to choose the appropriate disk. In our example, «disk number» is 0.

DISKPART> select disk 0

Disk 0 is now the selected disk.

Now seek out the partition we want to remove. This should be the partition shown in the first reagentc /info command. In our example, it was partition 4. Use the list partition command to list the partitions:

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    System             100 MB  1024 KB
  Partition 2    Reserved            16 MB   101 MB
  Partition 3    Primary             63 GB   117 MB
  Partition 4    Recovery           664 MB    63 GB

From the above output, it should be clear which partition is the recovery partition. The partition number should match the output from reagentc /info command earlier and it should show in the listing as a Recovery partition. In this example, we were expecting partition 4 and our listing showed that partition 4 is indeed a Recovery partition. Select this partition using select partition «partition number». In our example, «partition number» is 4:

DISKPART> select partition 4

Partition 4 is now the selected partition.

Now you can delete that partition. Note that the following command uses the override parameter. Be careful and double check what you are doing. The override parameter means we are performing an operation which DiskPart thinks is dangerous. Recall that the partition we are removing was originally used for the Recovery Agent environment which we disabled above. Recheck that the partition we selected is indeed the partition you wanted to remove. Ensure that if you have any data on your PC, you either have accepted that you might experience data loss or that you have backups and have verified that you can get data out of your backups. If you are certain, proceed with delete partition override:

DISKPART> delete partition override

DiskPart successfully deleted the selected partition.

You can now list the partitions to show the results using list partition:

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    System             100 MB  1024 KB
  Partition 2    Reserved            16 MB   101 MB
  Partition 3    Primary             63 GB   117 MB

We can see above that only the Recover partition was removed and the partition with data that we care about, partition 3, still exists. Proceed by exiting diskpart using the exit command:

DISKPART> exit

Leaving DiskPart...

C:\Windows\System32>

Reenable Recovery Agent Environment

I recommend that you turn recovery back on at this point. This will set up the Recovery Agent to use an image on your C: partition. If you need to expand your partition further again, this is more convenient than having a separate partition. However, while more convenient, using the C: partition does have its risks. Run reagentc /enable at an Administrator Command Prompt:

C:\Windows\System32>reagentc /enable
REAGENTC.EXE: Operation Successful.

Now check reagentc /info to see where it put the recovery environment:

C:\Windows\System32>reagentc /info
Windows Recovery Environment (Windows RE) and system reset configuration
Information:

    Windows RE status:         Enabled
    Windows RE location:       \\?\GLOBALROOT\device\harddisk0\partition3\Recovery\WindowsRE
    Boot Configuration Data (BCD) identifier: 815b3db2-d49c-11ed-be7f-00155d019403
    Recovery image location:
    Recovery image index:      0
    Custom image location:
    Custom image index:        0

REAGENTC.EXE: Operation Successful.

You can see from the above output that a path within partition 3 which, in this example, is the C: partition was used.

Expand Your Primary Partition

You may now use the graphical disk management interface to expand your C: partition freely