Increase c drive space in windows 10
If there is an adjacent unallocated space behind C drive, you can extend it in Windows 10/11 Disk Management. Here are detailed steps:
Step 1. Press Windows + R at the same time to open Run dialogue.
Step 2. Input diskmgmt.msc and hit Enter to open Disk Management.
Step 3. Right-click C drive and choose "Extend Volume".
Step 4. Follow the prompts that will appear to complete this operation.
Note: If the unallocated space is not adjacent to the C drive on its right side, the "Extend Volume" will grey out and cannot be clickable.