How to rename SQL 2012 Server Host name

Hello Experts,

I need to move a database application from an old SQL Server to new hardware.

The netbios name of the old server is "server2"

The netbios name of the new server is "server" ( I can't change this)

The database has to run on an SQL server\instance called "SERVER2\ABCSQL"'

Have a look at the attached screenshot. I have installed 2012 Express and created an instance "server\test"

How can I change the name from "SERVER\TEST"  to    "SERVER2\ABCSQL" ?

Preferably with SQL Management Studio as I'm not an SQL expert

thanks