Tilt up the front of the shelf and then lift the shelf straight up.

Pull the shelf out.
Tilt the front of the shelf up and guide the shelf hooks into the slots at a desired height.
Lower the front of the shelf so that the hooks drop into the slots.

Glass shelves are heavy. Use special care when removing them.
Do not clean glass shelves with warm water while they are cold. Shelves may break if exposed to sudden temperature changes or impact.