A nearly full system drive can interrupt updates and make routine work frustrating. Check what is occupying the space before removing files.
See where the space went
Open Settings > System > Storage. Windows groups files by type. Select Cleanup recommendations to review files you may be able to remove. Check Downloads and Recycle Bin carefully: they can contain important documents.
Use Storage Sense thoughtfully
Open Storage Sense from the Storage screen. Before enabling automatic cleanup, read its settings for temporary files, Recycle Bin and Downloads. If you use OneDrive, check whether cloud files will remain available offline.
Move or uninstall rather than guess
Move photos and videos only after verifying a backup. Uninstall unused apps from Settings > Apps > Installed apps. Do not delete folders inside Windows or Program Files to reclaim space.
Further reading: Microsoft Support: free up drive space.