Look for a loose edge on the decal. Slip your fingernail underneath it. Pull up the decal and remove it.
Apply warm soapy water to the decal. Allow the water to soak into the decal for 10 minutes. Pull off the decal. Slice lines in the decal using a razor blade for a stubborn decal. Add warm water to the decal again and attempt to remove.
Buy a professional grade glass scraper from an automotive store. Insert a fresh razor blade. Apply a commercial window cleaner and scrape decal off the window.
Clean the sticky decal residue from the window using a de-greaser. Apply according to the manufacturer's directions. Wipe it off with a clean cloth.
Wash the entire window with warm soapy water. Rinse and squeegee off the excess water.