If you already have a TrackMania² Canyon account then all you will need to do to add ShootMania is to enter your activation key on your ManiaPlanet Player Page.
Visit http://player.maniaplanet.com then highlight the Account button and select Player keys and enter your ShootMania activation Key. The next time you start ManiaPlanet you will have the option to load ShootMania into one of your stations.
Stations are placeholders within ManiaPlanet where you can load game titles, game mods, collections of maps, or even minigames created with Maniascript. You can unload a station by pressing the 'Del' key on an active station, but major stations like TrackMania² Canyon and ShootMania Storm cannot be removed.
Once you have downloaded ShootMania Storm, if the Joust and Elite titles are not present in your titles list, please restart ManiaPlanet and they will appear. Then you will be able to load Joust and/or Elite into a station.