First, select season mode. Next, choose a team, but do not select "Start" yet. Go to "Salary Cap" and change it to "No". Play all the games of your season. When a prmpt appears asking you to convert season to franchise, select "OK". Choose your team to play with again and resume to the off-season schedule. When you want to sign a player, you will see "No Cap" at the top. You may now sign anyone of your choice.