When the C: drive turns red, the fix is almost always four or five specific places rather than a general clean. Work down this list and stop when you have enough room.
1. Previous Windows installation
After a feature update, Windows keeps the old build so you can roll back. That folder can be 15 to 25 GB. Disk Cleanup as administrator, then check Previous Windows installations. Only do this once you are sure the update is stable — the rollback option disappears with it.
2. Hibernation file
hiberfil.sys is sized in proportion to your RAM, so 8 to 16 GB is common. If you never hibernate, disabling it in an elevated command prompt with powercfg /h off returns all of it.
3. Find the actual big folders
Settings, System, Storage shows a breakdown by category. Nine times out of ten the answer is downloads, videos, or a game library nobody remembered installing. No cleanup tool will find these for you, because they are files you chose to keep.
4. Browser caches and app data
A browser profile can hold several gigabytes after a year of use, and messaging apps quietly cache every image you have ever been sent. This is the layer BleachBit handles well — run it as described in the walkthrough.
5. Uninstall what you do not run
Settings, Apps, sorted by size. Trial software and old games are the usual suspects.
Realistic totals
- Previous Windows installation: 15–25 GB, once,
- Hibernation file: 8–16 GB, once,
- Temporary and update caches: 1–8 GB,
- Browser and app data: 1–5 GB,
- Uninstalling unused software: highly variable, often the largest of all.
What not to do
Do not delete folders inside Windows or Program Files by hand, and be skeptical of "registry cleaning" as a space saver — the registry is measured in megabytes. Full reasoning is in what you can safely remove.