Hm if this one works like all the others, ghostkid, you need to play story mode to unlock the capsules that allow you to change characters into SSJs. I remember in the last Budokai game, if you played both the Goku and Vegita storys correctly, you could even get up to SSJ4, so the same must be true for Tenkaichi.
Oh and here's a nifty screenshot for those of us who don't run that language of google:
"I've gotten 2,415 times smarter since then." -Master Control Program
and commanderViper, nope.. you cant change, in stead of the capsules you now have 'Z items' to bring up your attack; you also have standard attacks for 1 character you cant change them !! ??? CENSORED man, the camera S-U-C-K-S sometimes, only good thing is you can move free now and not just standing facing your oppenent, you can go and hide you after a wile the game gets boring but its a nice game...