I have an iPhone 7 (cracked screen) and i was wondering if i could upgrade to a iPhone 7 Plus or 8 Plus and how much money would that be?? My phone is unlocked, by the way.

We could not possibly give you an estimate here. Screen cracks vary in severity widely.

You might get an idea by a two-step approach:

• Figure the price of repairing a cracked screen: iPhone Service Pricing - Apple Support
• Get an estimate of the iPhone 7 Plus value: Renew and Recycling - Apple

So naturally you would subtract the cost of repairing the cracked screen from the iPhone 7 Plus value to get your credit amount idea. Then you would add the price of the new iPhone you wish to purchase.