There has to be a set screw (small flat head or allan screw) underneath the handle. It may not look like there is, but there has to be. Pull up on the handle in the open position and you should see the screw. (you may want to shut off the water to the house so you don't get flustered with the water running.
Unscrew the screw and should pull off. Try not to take the screw completely out of the hole.