Can I put my iPhone 4 sim into a iPhone 5s?

I have a iPhone 4 on tesco mobile contract and I know tesco doesn't do iPhone 5s on contract so I'm just wondering if I can buy a iPhone 5s as pay as you go and then put in my iPhone 4 sim and stay on that contract? I know there's a size difference between the sims but would I be able to get my iPhone 4 sim information put onto a sim for the iPhone 5s or would I just have to physically cut the sim?

The sim for the iPhone 5c & 5s is smaller than the one of the 4 and 4S. If tesco provides the nano sim you can get one from them and port your service from the micro to the nano.

When you get the new phone you can use iTunes to transfer the most recent back up from the 4 onto the 5, this will also transfer your contacts and internet favourites.

You just need a SIM cutter and you cut the SIM to nano-SIM and you're good. As long as the iPhone 5S is Tesco or unlocked, you're fine. Cut the SIM, put it in the iPhone 5S and activate. That's all. If you need iPhone 5S without contract or factory unlocked, mail me.