Pull out the desk drawer halfway and empty the contents out. This makes the drawer lighter and easier to handle.
Pull out the drawer completely, then back it in about an inch. Grasping each side of the drawer, lift it straight up and attempt to slowly pull it completely free from the desk. This will only work if your glides don't have stoppers preventing the drawer from being removed this way. Go slow if you're not sure how to avoid damaging the drawer or glides.
Look for small tabs or buttons on each side of the glide if lifting and removing doesn't work. Pull the drawer out fully, then feel around with your index finger or visually inspect the glides for the release tabs. Press and hold them as you pull the drawer out completely.