A clean install would be the best option, but if you're lazy like I was you can use the mklink windows command to relocate the files.
I have a 60GB SSD, and the only game I had on it was BF3. This was perfectly fine until expansion after expansion came out and before I knew it, HEYO! 500mb of free space left!
I did not want to reinstall the game and waste 20GB+ of bandwidth, so I simply used the mklink windows command to relocate the files to my D:\ drive, and it worked perfectly.
Basically, all "mklink" is, is a command line option to essentially redirect file access. The game is installed onto C:\, but when it goes to access it, instead it hits a redirection to where it is ACTUALLY located.
Think of it as just being a system level "shortcut"
Functionally, it will perform the same as reinstalling completely, you will move the game data to the other drive, but it will appear as a shortcut folder on your C:\ drive.