How do you free up system storage space in order to be able to upgrade software?

Copy all the stuff you do not need on a daily basis to an external drive.

Then delete them from your mac.

Movies, Music and Images take up the most storage.

• See used and available storage space on your Mac and the Official Stand on Managing Space Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

What is “Other” storage on a Mac, and how can I clean it out?

To see 32 bit applications before upgrading to Catalina and above Use Go64 to see who they are and find replacements of upgrades