On franchise mode, when going to player management, there is the spot where it has Potential and under it for other teams is ??.

Go to that and press X and it will sort them from A-F potential. This also works in Free-Agency.

You can also take players and move them from one position to another and it may change their potential.

And also if you go to edit player you can make a player that is a 95 line backer and put him at RB. Then then you can trade for them for practically nothing.