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Check the startup disk’s available space
Open Apple menu > System Settings > General > Storage. On older macOS versions, check About This Mac > Storage. If you can, note the available amount before changing anything. The storage screen and wording may vary by macOS version.
Review files you recognise
- Look through Downloads for old installers and archives.
- Check large videos, exports, and project folders you no longer need on the Mac.
- Review unused apps and old device backups using the relevant app or macOS Storage options.
- Check the Bin before emptying it; keep items you may still want to restore.
- If you use cloud storage, confirm what is stored locally and what is safely available online before removing a copy.
Use a folder scan to narrow your search
Mac Disk Space Helper scans a folder you select and shows which folders and files inside it are largest. This may help you review Downloads or a personal project folder. The app only reads sizes; it does not delete or move files, and it cannot remove every kind of data involved in an update.
Do not delete unfamiliar items in System or Library folders to try to force an update through.
Try the update again
Once you have safely made room, check Storage again and retry the update. Apple also documents temporary storage steps, including starting in safe mode; use Apple’s instructions if you need to consider that option.