Can i swap phones but keep the same contract?

I have a s7 on a 2 year contract with vodafone. Can i get a new phone e.g an iphone and continue my contract with the new phone - so i put the SIM card from my s7 into the new phone will it work? (If its unlocked to any services). Or would i have to pay to cancel the contract. (In the UK)

Yes

Yes. You have to pay full price for the phone and it must be SIM unlocked.