Is this CC or EA Store content?
If its from the store, then open you Sims 3 Launcher, click Installed Content, find the item you want to delete and check it, then click uninstall.
If its CC downloaded from the internet then you'll have to find the file in your The Sims 3\Mods\Packages folder and delete it from there. If you don't know what the file is called then I'm out of suggestions.