Summarize the following:
You will need a special windshield trim tool that you can slide under the windshield trim and remove it to access the clips. Once you have access to the clips, use the trim tool to carefully twist the clips loose. It may help to cut the gasket so that you can straighten it out as you pull. If any of the gasket remains stuck to the windshield you can clean it off with a glass scraper or razor. Just be careful not to damage the windshield in the process. Once you get this end secured into the groove that your old gasket was in, you can start working your way around the windshield slowly. Go around the perimeter of your windshield working the gasket into the groove and being careful not to miss a spot. The entire gasket should fit snugly into the groove. You want to put the windshield clips back into their original place and tighten them so that they hold the gasket and windshield securely. This trim covers your windshield windshield gasket and clips.

Summary:
Remove any windshield clips. Pull out the window gasket. Push one end of the new gasket into place. Work the entire gasket into the groove. Tighten the windshield clips. Replace the trim on along the perimeter of the windshield.