There are many ways- Involving Ammonia, Newspapers, Heat guns etc.
Easiest one is Water and a Squeege. Spray water, let it soak for a few minutes, then remove with Squeege. Squeege won't damage your car's windscreen- It's made of Rubber.
Best idea is to let a good tint guy do it for you, make sure to warn him in advance. It's their job!