Trade in

I’m currently on a contract with tesco and have an Iphone XS. I want to upgrade my phone but it’s £500 to end my contract. If I trade in my iphone XS with apple and pay £30(ish) a month for an iphone 11 do I take the sim card out my iphone XS and put into the 11 and continue on with the same contract and pay my usual £40 to tesco and the £30 to apple every month or do I need to start a new contract? I’m not sure if this is making sense 😂Do I also need to let tesco know i’m doing this? Hopefully someone understands my question. Someone please explain this to me.