How To Remove Garmin’s Adhesive Disk (for Handheld Gps) From My Car’s Windshield?

I stuck Garmin adhesive disk for handheld GPS onto my car’s windshield without seeing Garmin’s note that it is “permanent”!
I’m planning to sell my car and the buyer wants none of it!
What is the safest (/simplest) way to remove this dashboard adhesive disk?
Thanks!