Clean-up in aisle movies/TV

I am barely a newb user of Plex Media Server on a QNAP NAS.

For a long while I have been finding movies and TV shows and putting them on the NAS for personal viewing. But I would often DL several differnt torrents because I didn’t understand the different descriptive names. 720 or 1080 or ScreenRip, (YUCK! ) So, I ended up with a lot of trash which I want to delete from my NAS, but I don’t know a reasonable way to do this in bulk.

Seriously! I may have 5 different versions of a certain ST TNG episode, hoping that one would work, better than the other. Eventually I figured out I had a configuration issue which kept many from playing through my Roku. But now that I have that straightened out, I realize I don’t understand (or appreciate) how Plex decided WHICH version to play, when I click to play. Does it pick the highest compression with highest resolution? Last file put into the NAS?

Since I don’t know, I can’t even make a good choice in WHICH files to manually delete or leave!

Please point me to the docs which will help me, but I am too new to even know to search for?

Thank you to all of those who help on these boards.