I want to try Gclener but i cant seem to get it installed. Its downloading files but when i try sudo apt install gcleaner it says "cant find the package".
Correct; the developer only ever released a version for Ubuntu 14.04 Trusty Tahr.
I use Ubuntu Cleaner, which is listed in that article, or I use BleachBit, also listed in that article.
Whichever "cleaner" you use be careful you don't remove necessary files, dependencies or system directories otherwise you will find yourself reinstalling.
I use stacer and when i need a little more precision, bleachbit.
While installing something you discovered because it sounds good, it has a nice UI is appealing, most of the time you will find that using vetted software others recommend will work better than a version specific software that is no longer maintained.
You can install it once you downgrade your os to the supported version (not recommended due to security issues and no longer supported by the developers).