express renewal upgrade question

I am running norton internet security 17.8.0.5 (2010?) on 3 PCS and the subscription ends in 25 days.

 

If I want to upgrade to the 2011 version, must I buy the new CD or download the new software?  Or can I just purchase a new product key via the "EXPRESS RENEWAL" button and the new version will automatically be downloaded?

 

Also, if I do purchase a new product key using express renewal, I assume I can then use that new product key on all 3 machines currently running norton and they will be updated with new software, etc??

 

Thanks