I have a 2014 v6 pony package Mustang which comes with the factory wheels. I want to upgrade to some 20" wheels. Do I have to lift or change my suspension to do that?

 

No lift needed as long as you have a shorter tire sidewall. Places like Tire Rack or Discount tire should be able to calculate the tire size needed to maintain proper overall diameter and speedometer accuracy. If you have 17" rims, you want a +3 setup, 18" stock would be a +2. This site might help: https://www.tyresizecalculator.com