How do i change my roster?

I cant change the starting 5 on my game, how do i do that? Ive signed a new player and i want to move around who plays C and PF. I wan Emeka to play C, and i changed his primary and secondary position to C, and he still plays PF. How do i change that?

player rotation...

yes but in player rotation it does not place okofor at C, it has him at PF, even though his postion in C. And even if i want a player who is a SG to play PG how do i do it?

simply, you turn on the "assign playing time" for center and then choose playing time for Okafor