Once your hard disk is over 85% full, it generally won't be able to install new software.
https://grandperspectiv.sourceforge.net/
is a popular software to get a good overview of what's filling up space on your Mac. Keep in mind some things might be essential system files, which you wouldn't want to touch. iCloud backups and Time Machine backups that are interrupted leave behind large temp folders. IDVD has large cover art folders, which you can backup to external storage, and not have on your computer except when you need it, and put back in the correct folder at that time, and Garageband has large loops folder for use with composing music that does the same thing.
It is a good idea if you are going to keep a separate copy of such files, make a note of the full path it is found in, and create a folder named after the path without the forward / in the file name or periods.
Since your signature suggests you are running Mojave, be especially mindful that upgrading to Catalina and above, requires upgrading all apps to 64 bit release.
That's covered in more detail on my Catalina upgrade tip:
Catalina - an upgrade guide - Apple Community