How do I change windsheild wiper blades on a 1999 buick Lesabre?

It depends on which type of blades you have. But either way it is easiest if you turn the key forward to on position (not start). Then turn your blades on and when they reach the uppermost position turn your key off. Your blades should stop at that point. Then there should be a clip on the underside of the blade where it goes onto the post. push up on that clip and the blade should release. I recommend Rain-X brand blades for a replacement I have used all kinds of blades and Rain-X are the easiest to install and seem to wipe the best. That is if you have a loop type arm. If you have a post end its a litle different but if youn buy the blades there will be an instruction on the box that they come in. Or you can buy them at a carquest or auto zone and they will put them on for free.
How do I change windsheild wiper blades on a 1999 buick Lesabre?
I went to Wal-Mart and at the Auto. Department they installed my blades for free with the purchase of new ones .