What happens with "last months rent" if tenant resigns?

[Brett M.]

I had my tenants pay first and last months rent wen signing plus a security deposit.

Their year is almost up and they would like to resign. I gave them notification that I will be raising rent on this new contract.

Should last months rent that they paid in the beginning just get transferred to the new contract plus the rent increase? They were asking about not paying rent for this month since they already paid for it but then the would just have to give me a new last months rent on the new contract. Am I correct in this thinking?