In Manager mode, access the experience points menu. At the top of the screen is an option you can toggle if you want to have the experience points spent automatically. Turn the autospend off and save up until you have about 40,000 experience points, or roughly a third of a season. Then, go back into the menu where you spend your points. You can spend much more points in one go. This makes it easier to decide what aspects of a player to upgrade. When you have 40,000 experience points, turn on the auto spend. The CPU spends the points better if there are more to spend.