Should be staked in. On some of the taller sights, some folks recommend taking a pair of vice grips and gently rock the sight back and forth until it snaps off and then driving the tenon down into the slide and out the bottom.
On the smaller GI sights, and the way I do it, is to drive out the tenon from the inside out.
As for installing a new sight, some folks use red lockite when they stake the replacement. Others do not. A staking tool will set you back between $15 and $35 depending on the model. I have heard the Trijicon/MMC tool is very nice, but I used the Kings tool. You will also need a dremel tool to dish out the inside of the slide to give the new tenon a place to flow when you stake it and then grind down excess to allow the bushing to fit.
Seems most smiths charge about $15 to install a new one and about $40 or so to do front and rear sights. Pick your poison.
While it's an easy job, if it's a one time thing and you know a smith local to you, I'd just pay someone to do it.
You'll also hear that only silver solder and/or a dovetail will work, but I'm still waiting to see all the 1911's missing front sights.
