Using long nose pliers, squeeze the locking tabs on the mounting studs. While you do this, with your other hand pull the board gently outward so that the board won't slip back over a stud that has been released.

Lift the area of the board closest to the stud to free it from the mounting studs

Repeat this process of each mounting stud. until the board is free of each stud. Remove the board.

Try to work from one corner of the board down one side, then across. That will make it easier to maintain the gentle outward pressure and prevent the board from slipping back over the studs.