Uninstalling a Mod
To un-install a mod, simply select the mod in the list of installed mods on the right hand side of the tab page, and click uninstall.
Uninstall deletes all of the mods files, including the mod's entire "home" directory (My Documents\Bioware\Dragon Age\AddIns<mod_uid>). If you are a builder and have additional files in there, you will want to back them up first.
Under the hood, the uninstall process removes the mod from the AddIns.xml file FIRST, and then deletes the files. Generally if the un-install indicates a failure, it means there was some issue deleting the files. 99% of the time, the mod will still be removed from the AddIns.xml file properly, the error just means some files may be left lingering.
NOTE: The Dragon Age Toolset must be closed before uninstalling a mod, or else DAModder will be unable to modify the files.