I would like to know the same as I can do and to upgrade 5.1 to 5.1.1 Epo.
on the same server Console Epo working with OS Windows Server 2008 R2, and my SQL 2005 data base working on a virtual server, which critical points have to be considered, also has nine branches working as distributed repositories and on the server console Epo is the Main Repository.
The first thing I would do is upgrade your SQL from 2005 to at least 2008 R2 or 2012. Backup the DB, detach it, install new version of SQL, then re-attach and configure as needed.
After that, then I would do the upgrade to ePO 5.1.1 - go through this KB to make sure you have everything met before doing the upgrade.
I'm not sure I understood you exact question, but the upgrade is pretty straightforward and simple from 5.1 to 5.1.1