From another site
Windshield: Rubber seal type
You will need:
A strong thin rope about about 15 feet long
A helper
A slippery substance like dish soap, but preferably KY jelly type lubricant which is water soluble and doesn't leave a sudsy mess when washed off.
A rag
Water
If the rubber seal has an insert strip, install it first.
Fit the seal around the windshield.
Wrap the rope tightly all the way around the groove of the rubber seal, making sure the rope ends overlap. Let the ends hang on the inside part of the windshield.
Apply lubricant to inside part of the seal which will contact the window opening on the vehicle. Applying lubricant to the opening will help too.
Place the windshield on the opening of the vehicle.
Go inside the vehicle. You will be pulling on the rope. Before you pull, have the helper apply mild pressure to the area were you will be pulling on the rope.
Pull the rope toward the center of the windsheild. The seal should start slipping over the ledge and hug it. The helper should be applying mild pressure just ahead of you.
Go all the way around until you've pulled out the entire length of the rope.
Wipe off lubricant with a dry rag, wash off the remainder with a wet rag.
*Do not store lubricant in your tool box. Your friends will not believe you when you explain what it's for.