Remove the existing shelf in the cabinet. Lift the shelf up off of the supports and then pull it out of the cabinet opening.
Pull out the existing shelf supports and see what type of material they are made from. Older cabinets may have wood dowels or metal supports. These will need to be discarded in order to use clear plastic shelf supports.
Measure the width of the cabinet side panels to determine the size of shelf support that you will need for your glass shelf.
Insert the shelf supports into the pre-drilled holes in the cabinet to make sure they fit correctly.
Place the glass shelf on top of the supports and check for levelness.
Set a level on the shelf and see if the bubble indicator indicates that the shelf is level.
Reposition the shelf supports, if necessary, to level the shelf.