My 1990 geo prizm is overheating my cousin thinks that it's the thermostat. How do i replace a thermostat?

Hello Guest and thank you for asking your question, on Fixya.

Here is a simple process that will walk you through a few steps that will pinpoint the overheating problem on your 1990 Geo, without even using any tools. It has helped millions of people, and I am certain that it will help you, because I wrote it for people in your exact situation.
How to diagnose your overheating Geo

Get more great (money saving) tips and tricks about your vehicle from: twitter.com/acoates23234

Thanks for the vote, and good luck!