This is a good article about backing up your data and keeping your systems clean.
A utility that I like for Windows cleanup is Piriform's CCleaner free.
A utility I like for Mac is YASU, Yet Another System Utility. It's pretty inexpensive and does a good job. (The Mojave version hasn't been released yet, but should be soon.)
Any questions about these issues, contact me, firstname.lastname@example.org