Configuration Manager 2012 - Upgrading Your Clients to SP1
From the archive (2013). Written for the tools of the time, so some details may be out of date.
Below are some links to a couple of methods for upgrading your ConfigMgr RTM clients to SP1.
Great post by Nickolaj Andersen (fellow MVP) on how to upgrade your clients to SP1.
Another fellow MVP Peter Daalmans also have a post on using the automatic client upgrade process.