System files taking up 90% of space! Help!

[AC Question]

Ok. I'm pretty tech savvy. I mean, I just moved six apps that wouldn't allow me to move them to my SD card, onto my SD card manually (using APK downloader and my computer. Yes they all work just fine.) But the BIGGEST memory hog is freaking System. I have a Galaxy s5, updated to the latest (I think Marshmallow?) and it seems ridiculous to me that System takes up literally six gigs. There's no need for that when at the time I got it (before the newest update as of 04/2017) System took up less than a gig. I know I can go into storage -> internal storage -> explore -> back (it takes you directly to "my files")-> device storage and delete a bunch of those files in there and that would probably fix the issue. My thing is, I am NOT savvy enough to know what files to mess with, and what files to not touch if I ever want to use my phone again. I definitely don't want to root my phone and risk bricking it (though I would LOVE to uninstall all the stupid Verizon/Google/Samsung bloatware. -.-'). So I was wondering if anyone knew enough about Android and specifically Galaxy S5 to be able to give me at least a general list of files I should and shouldn't touch. I can give screenshots of the files listed to help out. I just really want my memory back so I can actually store photos on my phone once in awhile.....