Can I upgrade my iphone from Sprint?

I just got my iphone last week and its an iphone 4 with 8 gigs and i already used half the memory with pretty much just music alone. I know there's no way to install new memory but if i were to switch from 4 to 5gen could i do it then? Cus they don't make 4 anymore, so should i just wait for the 5th gen to take over and replace it then?

Added (1). But if I trade it in I think theyll still give me 4 gen so should i wait until they're completely out of 4s?

What are you talking about? The iPhone 5 has been out for a long time!

Normally, carriers allow you to return a phone within 30 days of the purchase date, so you can still return it and exchange it for an iPhone 5. You'll have to pay the difference though - which is about $100-$200.

It would work since the iPhone 5 has a minimum of 16GB, giving you double the memory.