This trick works in Manager mode when you are changing teams at the end of a season. At the end of the season when you are asked whether or not to renew certain players' contracts, choose not to renew the contracts of your favorite or best players (the ones you want on your new team). When you arrive at the new team and the transfer period starts, the players will be free agents, allowing you to transfer them without paying millions in fees and allowing you to re-negotiate the contract to fit your new team.