i also recommend the mgw sight pusher i just received mine yesterday from amazon.
now on amazon it is listed as: Trijicon GL02 Night Sight Installation Tool Kit for All Glock Models
but it is actually the mgw sight pusher and it has a front sight tool as well.
amazon also has some that are discounted due to blemishes mine was listed for 110.00 when they are normally 130.00 (i used the cash i saved on the tool to buy the defoor sights)
the only thing wrong with it was the box was dented there is no damage to the tool itself not even a scratch.
i have already installed the defoor sights using the above tools and it was a breeze.
The MGW Pro is the way to go. I bought mine about a decade ago and it has served me well. I have seen them on sale for as little as $80. Some folks will loan theirs for a very small fee. In the absence of one, you can use a nylon or brass rod to 'push' the rear sight out (left to right) and seat a new sight. The pusher is best for night sights (glass vials). But it is possible with a rod and 'gentle' taps.