In the middle of this myself. Barclays app let’s you select which product you want to roll into once your current one ends. Takes maybe 10 minutes to get that sorted, then it’s on you to monitor their rates online incase they drop. They won’t go out of their way to tell you if they do, but you can call and amend to any new cheaper deal if one comes up.
You can start this process 6 months before your deal ends, so we got our next rate provisionally booked in during march to start in August.
You want to do the final check to see if there is a better rate about a week before your deal is ending