You can extend C: only when D: is a volume on the same physical disk and deleting it creates unallocated space immediately to the right of C:. Back up D: first because deleting the volume erases it; separate disks or intervening recovery partitions cannot be merged this way.
Copy every needed file from D: to a verified external drive or cloud location and open a few copied files. Do not continue with the only copy of any document, photo, project, save, encryption key, or recovery file.
2
Open Disk Management
Right-click Start and choose Disk Management. Use the lower graphical view to identify Disk 0, Disk 1, C:, D:, recovery partitions, and the exact order of the volumes.
C: and D: must appear on the same Disk number. D: must sit immediately to the right of C: after deletion; if another partition is between them, Disk Management cannot extend C: into that space.
4
Check encryption and applications
Suspend or document BitLocker recovery information when applicable, and move applications or libraries that depend on D:. Do not delete a manufacturer recovery volume, EFI partition, or a D: volume on another physical disk.
5
Delete D: only when safe
Right-click the confirmed D: data volume and choose Delete Volume. Read the warning, verify the drive letter and disk again, and continue only when the backup is complete; this action erases the volume.
6
Extend the C: volume
Right-click C: and choose Extend Volume, then add the adjacent unallocated space. If Extend Volume is unavailable, stop: the layout does not meet Windows' requirements and forcing it with an unknown partition tool risks data loss.
7
Verify Windows and restore files
Restart Windows, open File Explorer, and confirm the new C: capacity. Restore only the files you need from the backup and update any application paths that previously pointed to D:.
Video walkthrough
If it does not work
If C: and D: are on different physical disks, keep them separate; the Windows system volume cannot be safely merged across those disks with this procedure.
If a recovery partition separates C: from the unallocated space, do not delete it casually. Keep the backup and ask the PC manufacturer or a qualified technician to review the exact layout.
ⓘ Sources and verification
Checked against official documentation on . Scope: Windows.
Follow the linked first-party guidance if labels differ after a platform or app update.
