SQL Server: is it to drop a SQL Server 2005 by sqlcmd or set an instance to SQL Server 2012?

I have a problem I have an instance called SQLEXPRESS previously created by SQL Server 2005 Express.

Now it is uninstalled but it didn't remove the instance.

How can I remove it and after to create it with an instance of SQL Server 2012?

The instance is: AC5099\SQLEXPRESS

Thanks