I want to upgrade to Monterrey but message says not enough space, but I have enough icloud memory

Having space on iCloud doesn’t really matter. To upgrade your computer the internal hard drive needs enough space to hold the installer file plus extra for the installation process. About 20GB of free space in total though there are circumstances where more may be required. kai-k suggests moving some files to your iCloud and deleting them from your internal drive which can be a bit risky if you aren’t very very careful. A better solution would be to back up your hard drive to an external drive using TimeMachine. Then you can safely delete files from the computer’s internal drive for the installation and then restore them afterwards. This provides a double safeguard - it is safer than that moving things to iCloud and gives you a backup in case the upgrade goes haywire.

Hi,

Try to move big Photos or Music Library to iCloud space and delete it from internal drive.

Then upgrade to Monterey after that moved to iCloud Library back again to internal drive could works.