Okay, hit the yellow upgrade button. Itll ask for another five bucks, or one if u payed a while ago, and hit pay. Dont worry, it wont take ur money, itll realize u already payed and give u the upgrade free.
U can't? Wow , that's just how crappy my phone is then. I've played on my dad's iPad and my phone (sorta) at the same time. Lol, my phones so slow it couldn't tell the server that it was logged in I guess.