A nearly full C: drive can make Windows feel slow and can prevent updates from installing. Start by checking where the space is going; do not delete folders you do not recognise.
1. See how much space is left
Open File Explorer and select This PC. Under Devices and drives, check the free space on C:. If it is very low, aim to make room before trying a Windows update.
2. Use Cleanup recommendations
Go to Start → Settings → System → Storage → Cleanup recommendations. Windows groups items such as temporary files, unused apps, large files and cloud-synced files. Review each group before selecting Clean up.
3. Turn on Storage Sense
In Settings → System → Storage, turn on Storage Sense if you want Windows to regularly remove temporary files and older Recycle Bin items. Read the options first so it does not remove something you intended to keep.
4. Review Downloads and large files
Open Downloads, Pictures and Videos in File Explorer. Switch to Details view and sort by Size. Move files you want to keep to an external drive or a trusted cloud location; delete only files you have checked.
5. Empty the Recycle Bin
Files are not fully removed until the Recycle Bin is emptied. Open it, check its contents, then choose Empty Recycle Bin.