You should just need to re-install it from the place you got it originally (the Play Store?)
Unless you mean something different from Launcher to what I understand. In that case, you could try a factory reset.
First, you need to back up all your data, ensure all the Google sync options are set and everything has been sync'd (go to your account via a browser and check contacts etc are all there).
To do the reset (I don't have your phone so it may be slightly different):
Settings
Backup and Reset
Factor data reset