I have a cracked iPhone 5c can I upgrade at&t?

I have had the 5c for like 1 and a half years it's cracked could I get a iPhone 6 how could I let me know I have at&t

Sure, if your contract is paid up or your phone purchase on the 5C is paid off. You can then get any other phone you want. If your contract or phone isn't yet paid off, you'll have to pay it off before getting a new phone. Your 5c might have some trade value, which will help with the new phone purchase. Otherwise, simply take your 5c to a local phone repair shop and get it fixed.