I am eligible to upgrade and I just want to know how much it will cost to upgrade to an iphone 6 from a Samsung galaxy 4
Hi israel. Please try the link I provided above. I tried it and it tells me that a Sprint Samsung Galaxy S4 that has no damage will be credit $60.
So you want to trade in your phone to get an Apple iPhone 6? Check out Sprint Buyback Program page (link) and see how much will they buy your phone.
Hope that helps!