Hi DeAnna

The first thing to do is to try and remove files not required - archived course, old course backups and the Cleanup task under Server can be used 

You can see the file size using the file picker  this can also be used to delete files. Remember that deleting the files is permanent so backup before deleting 

I can't see a way in Totara to see the overall file size of Totara this is more on the web server admin and database server admin  side 

regards