Go to the "Office", and find a player which is nearly at peak level and sell him. Sell him
to a team that is not a rival team so you may be able to get him back. View his status
under "Team Management", then select "Player Growth". At the next transfer season buy that
player again after his peak has been reached. Buying him will increase his overall rating.
(Note that it can only be done one time). To have him grow faster, go to "Office", then
"Calendar". Schedule some training to make him grow. Do not train too much or it will
affect their fatigue.