Is it possible to rename an SQL Server 2012 Express instance?

I have a MySQL background, so when I installed SQL Server 2012 Express I wrongly put my desired database name as the instance name.

I guess I want a single instance installed and then each App would use it's own database on that single instance.

How can I change the instance name to something generic (the default)?

As I said I'm using SQL Server 2012 Express, and this is the only instance and version on the computer.