Normaly when you want to upgrade from Lync2010 to Lync2013 and if this is a Enterprise Ed, you have a SQL server running. You have your Lync2010 on a instance.
Well and this is your only SQL, well then you have a challenge.
Even if you create a new instance on the SQL it will tell you that your user database is on the server and is in use.
It is two ways to get out of this as I sees it:
1. either you can install a Lync2013 Standard Ed and use a local SQL express.
2. you can build a new SQL server and install Lync2013 Enterprise Ed.
If anyone else has come up with some other solutions please post a reply on this post.