Reinstalling a fresh Version on iPad

Hey - hope someone can help me out.

A friend got me into Empire Z so i could join his alliance. I went ahead and built up my character to level 7, only to discover that I could no longer transport to a different world (to join my friends alliance). I've tried deleting the app (always choosing to remove data from Game Center), reinstalled - but it still picks up from where I left off. I also installed it while logged out of Game Center, which allowed me to start from scratch, but once I logged in to Game Center in a different game, went back to Empire Z - I was right back where I left off at level 7.

So ... is there a way to transport to another world after level 6/7? Or does anyone know how I can completely wipe my game so I can start from scratch?