First you need a new windshield. Urethane, spatula, hammer, gasoline, some old fabric and a helper.
1.- Remove the windshield wipers and the grill that covers the bottom of the windshield, you will see the 2 plastic bases where the windshield stands.
2.- Remove the plastic surround side and top mouldings, do it gently since the plastic can be old, you're going to use it again.
Step 1: Glass detachment
Separate the glass from the urethane, since the urethane is very strong, use a hammer and a spatula (this need to be done gently since you don't want to damage the paint)
This is where the helper is needed because he is going to tell you when to stop, when he sees the spatula blade out, he's also going to tell you where is not finished.