Rétablir un site (Office SharePoint Server)
On the top link bar, click Operations.
On the Operations page, in the Upgrade and Migration section, click Site content upgrade status.
On the Site Content Upgrade Status page, next to the URL that contains the site you want to revert, click Continue upgrade.
On the Site Collection Upgrade page, on the Actions menu, click Revert site.
On the Revert to Non-Upgraded Site page, in the Select Upgrade Site Collection section, next to Site Collection, click the menu, and then click Change site collection.
On the Select Site Collection page, click the site collection to revert, and then click OK.
On the Revert to Non-Upgrade Site page, click Continue.
In the message box, and only if you are sure that you want to revert this site, click OK.