You need to obtain a taller front sight or a shorter rear sight. The other option is to simply shorten your existing rear sight.
If you go with the second option, use duct tape or masking tape to protect the slide from an errant file stroke. Only make a couple of strokes with the file between shooting groups to make sure you don't take too much off. I don't have the correction formula handy, but you should only need to remove a few thousandths.
