Hi James...
I would be very surprised if you can't!
If you look to the left hand side of you screen down the bottom you will see ACCOUNT SETTINGS...
Click on it and I think you will find where you need to go from there...
You will see BILLING DETAILS & where you can update.
If you have any problems you can always throw the question out to the community...you will get a faster response by doing that...
You could be waiting ages for someone to answer your blog!
Best wishes
Steve

I saw this answer from another member!

Top right,
Click on your picture then on account settings then on Subscription.
You can change it there.
Let me know if this helps,