I've done what you suggest, and I don't see a "Renew" button either.
The following is how I got mine renewed.
I see my three profiles (companynameProfile, "Team Provisioning Profile", and productnameProfile). THe first and third are going to expire within a couple of weeks. The second (and only the second) is flagged as "managed by Xcode". The profile names appear in a table with columns labelled: "Provisioning Profile", App ID, Status, and Actions. The status for all three is "Active". First 1 and 3, the Actions column has a "Download" button, and an "Edit" link. For 2, gthe Actions column has only the "Download" button.
There is no "Renew" (or "Refresh") button / link anywhere (and I did a view-source and searched that too :)
So, I thought...click on "Edit" on #3 ... two choices pop-up: Modify and Duplicate. I chose "Modify"
There is still no renew/refresh ... but there is a "Submit" button ... which doesn't work (turns out its sort of grayed out, but that's not at all obvious...bad UI design).
I discovered that if I change something on the screen (in my case, I selected a previously unused device), "Submit" darkens (becomes available). Click on "Submit". You're quietly (another UI problem :) taken back to the prior page, and the "Download" and "Edit" buttons are gone, and the status column should say "Pending"!
After awhile, I refreshed the window (reloaded) (don't know if it would have auto-refreshed) ... and saw that the status column had changed to "Active".
Now...I downloaded the new profile (the one that the darn page doesn't tell you is new, and doesn't LIST THE EXPIRATION DATE so you could tell yourself ... third UI flaw already :)
I downloaded the profile, deleted the old profile from the list in the Organizer window of Xcode, then dragged the new one into the Organizer window of Xcode, and ... voila, Organizer shows a new expiration date (of about 3 months from today).
Hope that helps,
Stan Cupertino, CA, USA