First off, there are two types of staked sights. The Series 70 and prior has a skinny staking post whereas the Series 80 has a larger post. Both will come off the same, assuming someone didn't solder it in. Remove the slide and take the barrel / bushing out. Look directly under the sight from the inside the slide and you will see where it is "riveted" in. Grab the sight with a pair of plyers and rock the sight to the front and rear. It will loosen up the peened "head" inside the slide. Use a punch or a staking tool to drive the sight post out. Use a jeweler's file and carefully file the excess head, then use the plyers again to remove it. Be careful not to damage the finish on the gun.
Clean out the sight channel then insert the new sight. Place the slide on a piece of flat steel or an anvil, bottom up, where the front sight is resting on the steel plate. Use a staking tool and slowly "rivet" the post head until the sight is nice and tight. Use a jeweler's file to dress the excess metal so the bushing will go in without hitting the sight post.
Like a lot of things, there is a trick to riveting the head. Don't try to stake it with one or two hits. Rather, use the staking tool to gradually work the rivet head.
Staking tools are available from Brownell's. I used a home made one for years and finally broke down and bought one. The staking tool allows you to get a "straight down" hit on the sight post. If you try to hit it from an angle, you will ruin the sight. See:
http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=916&title=1911+AUTO+FRONT+SIGHT+STAKER
