Donald, I have had great success with "Hardened Arms" Uppers. You can't beat the quality for the price. You can browse AR15 Uppers here : hardenedarms.com/ecCat_27?gclid=EAIaIQobChMIjODTnKTm4AIVCV8NCh2PcwO9EAMYASAAEgL_mvD_BwE

Changing uppers, Donald is easy. Which upper you choose depends entirely on what you want to use it for with the new upper. Do you want a new upper with a target barrel? A new upper in another caliber? I use JSE Surplus a lot, and have had great luck with their products. They can supply virtually all your AR needs, at a fair price, and their service is top notch. jsesurplus.com/ar15uppers-readytoship.aspx.