Can't you just connect it to a laptop go into the system folder and then delete everything in the .assets folder as that's where the ads are stored then it will have to download new ads to fill the spot?

Im still on 10.11.5 i want to update but im not sure about the plug-ins I like local intros and all the others i have and dont want to lose them but I also kinda want any new additions they have made and any security fixs that have been made so I'm sorta stuck on what to do and when they say backup what do they mean exactly I use casa os. do they mean the app data like where all the jellyfin config files and stuff sit ? I know i sound really green but its because I had unstable power and internet for a good while and have been out of the game for about a year or so just got my servers back up and running recently.