It should be automatic renewal. The email I got said:
"The Season Ticket renewals window for the 2025/26 season closes today, and your Season Ticket will automatically renew between 13th and 14th May.
You do not need to take any action to renew your Season Ticket for the 2025/26 season. However, if you would like to make changes, such as changing how you pay, or your Cup Schemes, you must do so before midnight tonight (due to the bank holiday within the renewals period, we have extended the deadline)."