To install use the daupdater.exe application included with Dragon Age. Run that program and use it to install this downloaded file.

To uninstall you can either disable this mod in your Downloadable Content option of the Dragon Age main menu, or just remove the rngr_trng_cfm folder under Add-ins. If you manage to acquire the Ranger's Hood custom item from this mod, you will either need to delete it or keep the mod installed.