I cannot update my computer because it says no enough space how can I fix this problem

Follow these instructions: Free up storage space on your Mac - Apple Support

If you still do not have enough free space you can get an external drive and move data to it.

Freeing up storage, if that is your issue

Freeing up disk space - Time Machine snapshots

tmutil listlocalsnapshots /
    Snapshots for volume group containing disk /:
    com.apple.TimeMachine.2021-04-01-142742.local
    com.apple.TimeMachine.2021-04-01-163342.local
    com.apple.TimeMachine.2021-04-01-174425.local
    com.apple.TimeMachine.2021-04-01-192243.local
    com.apple.TimeMachine.2021-04-01-203820.local
    com.apple.TimeMachine.2021-04-01-222814.local
    com.apple.TimeMachine.2021-04-01-232930.local
    com.apple.TimeMachine.2021-04-02-002823.local
    com.apple.TimeMachine.2021-04-02-012748.local

tmutil deletelocalsnapshots 2021-04-01-142742 # deletes 1 snapshot

tmutil deletelocalsnapshots /   # deletes all the snapshots

Also see:

    diskutil apfs listSnapshots /

Finding what is using storage in your home directory/folder:

    du -hx $HOME | sort -h     # This will take a few minutes

The 'du' (disk usage) command will show storage being used in every

folder under your Home Folder. After checking for local APFS

snapshots, there is a reasonable possibility your Home Folder tree is

where most of the storage is being used. You can specify other

starting folders.