You can buy a n highly rated CHEAP cleanup app for $2.99 at the App Store There is a variety of software that automates the cleanup process. (Never use the on/off button to shut your Mac down, unless you are NOT able to do anything else.)

Now RESTART your Mac Menu:  > Restart.

Remove files and programs you 'stored on the desktop' Move them to folders in the Documents folder or on an external drive if you want to save them.

Your Mac will enter a maintenance mode and check for errors and will attempt to fix them. Shut down your Mac by holding down the 'ON/OFF' button for 11 Seconds

(You will not be able to quit the 'Finder').

Then still Holding down the command key ⌘ press the q key (Command ⌘+ q).

If your Mac is 'Frozen' -No Mouse and no Keyboard response.

Shut down ALL programs that are running.

This 'goal' is really impoertant If you have a small system drive. NOTE: Your primary 'maintenance goal' IS to keep your 'Macintosh HD' AT LEAST 15% Empty. Download the file double click it and it will install in your calendar app. In the right hand column is a calendar app that notifies you when to do your Mac Maintenance.

System maintenance for mac