In Impulse you have to change your 'My Games' directory.
Click on the Impulse 'orb' in the upper left...
Select 'File Location'...
Change the folder to 'My Games' and put in the directory you want the game installed.
You'll have to uninstall and reinstall the game to move it.
You could /probably/ try archiving it first (right-click o the game and choose 'Archive') and the uninstall and reinstall to save having to download it again. not sure.