You upgrade a SharePoint Server 2010 server farm to SharePoint Server 2013. Several users report that
a site collection site has the visual elements of SharePoint Server 2010.
You need to ensure that the site collection uses the visual elements of SharePoint Server 2013.
Which cmdlet should you run?

A.
Repair-SPSite

B.
Restore-SPSite

C.
Upgrade-SPSite

D.
Copy-SPSite

Explanation:
The Upgrade-SPSite cmdlet starts the upgrade process on a site collection.
The Upgrade-SPSite cmdlet activates the upgrade process for the specified SPSite object. You can also
use this cmdlet to resume failed upgrades. When you use this cmdlet to initiate upgrade on an SPSite
object, the object can be either a build-to-build or version-to-version upgrade. By default, the UpgradeSPSite cmdlet operates as a build-to-build upgrade. This prevents unexpected version upgrades of site
collections if you use this cmdlet after a patching operation. When in version-to-version upgrade mode,
site collection health checks are run in repair mode to ensure that the site collection is healthy enough
to upgrade successfully. If successful, the remainder of the upgrade occurs.