Upgrade

Hi There, I am a business 12 user on my first year and have recieved the email to upgrade to 13 but my question is simply do I have to upgrade or can I stay on 12? Will my account stop working after my first year ? As I didn’t realise it was a yearly subscription or is it not ?
I know it’s a simple query but just couldn’t see where i capsule get this info

Many thanks in advance
Mark