Change SQL Server version

I have both SQL server 2012 and 2014 installed. But when i open SQL server 2014 and check the version it returns:

Select @@VERSION

Microsoft SQL Server 2012 (SP1) - 11.0.3153.0 (X64) 
Jul 22 2014 15:26:36 
Copyright (c) Microsoft Corporation
Enterprise Edition: Core-based Licensing (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1)

So, i'm still running the SQL 2012 engine.

What do i have to change to run SQL Server 2014?