How to network unlock an iPhone 4s?

My partner has an iPhone 4S and wants it unlocked from Tesco, how does he do this?

If yours is not a stolen iPhone maybe you should try this. Switch to recovery mode simply by pressing an off iphone on the power and home button at the same while cable connected to your PC. Once you have successfully done that, iTunes will pop up for a factory restore request (network connection is required).

Ask Tesco to unlock it.

"I do not steal lol it's my boyfriend's and he wants to sell it as the contract is up. "

Then ask Tesco to unlock and there should be no cost.

Jailbreak it