You can upgrade through the mog station to a collector's edition. You will just have to pay extra to get it but once you do it, your PC game will be upgraded to a collector's edition.

I'm guessing you want to get the game because of the Steam sale but unfortunately I don't think you can't "upgrade" your current PC game using the Steam CE version. That would just add a second PC version to your account and the bonuses won't be added to your current characters.