Score the paint along any window trim, using the razorblade. This will prevent the paint from being pulled off the trim when you remove it from the glass.
Put on a pair of thick leather work gloves to protect your hands.
Use a heat gun to soften the paint, keeping it in constant motion until the paint begins to bubble. Keep the heat gun at least 4 inches from the glass surface.
Turn off the heat gun and set it aside.
Scrape paint off the glass, using the plastic paint scraper. Reheat the paint as needed while you scrape.
Remove any stubborn paint by scraping gently with the razorblade. Save this step for last to minimize the risk of scratching the glass.