"Unfortunately, the process android.process.media has stopped" on android lollipop.

I've been looking everywhere for the solution to this but all the previous solutions are on older versions. I don't have the ability to find my download manager in applications and I don't know how to clear the cache. The error pops up every few seconds

Welcome to the forums. What device do you have? Are you using an SD card? In most phones you can clear cached data in settings - storage. The steps to wipe the cache partition will depend on which model you have.