Package files can be either found in your mods folder OR they came with a Sim directly. Either way, you will need to do the binary-search method (aka the 50% method) to find the guilty party. Skins ALWAYS come this way unless you put them in yourself. Once you identified them, you can simply delete (or move) the file you want to get rid of.
Make sure to delete your cache files afterwards. If you are using Scripting Mods (like the ones by Twallan, Buzzler or treeag) make sure that you read the description of the mods. There are certain mods that need some extra steps before uninstalling them. Those file need to be uninstalled from your launcher. Make sure, you check your Installed Content and not Downloads. Also make sure that you have the tab with the Infinity Symbol to see all your installed stuff.
