Step One:
From the dashboard, click the "Club Management" tab, followed by "Roster Builder"
Step Two:
Select the "Event Roster" in the dropdown and click "Submit"
Step Three:
Click the "Red X" next to the players name that you are trying to release, then click "OK".
Note: If you do not see a "Red X", its because that roster is locked by the league. You need to contact the league to find out their specific process on releasing a player.