It is fitted in a dovetail - remove by driving from the left side ( if you're holding the gun) towards the ejection port side. Use a heavy vise bolted to a solid bench or don't even try it. If you don't need to change the sight then leave it in place and Park the whole slide. If a proper degreasing is done there won't be any oil left under it. I use solvent then acetone then high pressure air. If the sight is loose then look at new ones.