After you finish a game in Manager mode you will see the player rating screen. Scroll down to one of your players and press the Circle (player bio). When his stats, appear press the Back and your player rating for the entire team doubles. Keep repeating this until the match experience is full. You will then see that his stats have gone up by two every match. When his stats for that position are full, swap strikers for your defenders and their stats will go up in the opposite way.