Easy.Take a small set of vise-grips and clamp on to front sight leaving enough room between the jaws and slide as not to mark it up. Wiggle it back and forth and pulling on it at the same time until it breaks off,then take a small punch and drive the tenon thru the slide from the top.Sights are soft as the are peened from the bottom.Putting a new one on requires a sight staking tool or you can have it dovetailed.Kings has a reasonably priced tool with pretty good directions to reinstall.
First you may have to remove some metal on the underside of the slide GO SLOW. Place slide in vise and place dowel rod behind front sight. Pry gently with vise grip on old sight.
I then recommend you find a local gunsmith or machinist and have a dovetail cut for your front sight. This is a much more secure way. If you are going for the original look of a 1911 then for sure get a stake on tool and make sure the tenon is the correct size for your sight.