I could probably try to show you how to do it, if you want. At least if you use Windows 10 - I’ve done it once already with a friend who swore up and down that manually installing addons was too complicated for him when he couldn’t find an addon he wanted with the curse downloader. I’ve never used it myself, so it’s literally second nature for me now.
At the end of the day, all it is is downloading the file, opening it and taking what’s inside - in TRP’s cases the files named “TotalRP3” and 'TotalRP3_Data" and moving them into your WoW folder. Find your World of Warcraft installation folder, then go into interface - there should be a single folder in there named AddOns. Just take those two folders, put them in, then log into the game - when you get to the character selection screen, there should be an option at the bottom left to toggle or untoggle addons.
As to uninstalling them, it’s literally just going into that same folder and deleting what you put in. Boom, done. WoW handles the rest.
Oh, also. Unless you’re willing to take serious risks, don’t download anything that isn’t from this domain -
https://wow.curseforge.com/addons . ModDB is used a lot too, but I’ve never used it myself, so I cannot personally verify how safe it is.