In Hyper-V on Windows Server 2012R2 you are able to create the next generation of VMs – Generation 2, which is without legacy components. Those machines works better, but you are unable to transform existing VM from Generation 1 to Generation 2.
However, Microsoft published a script, which transforms VM, form Generation 1 to Generation 2. It is not an “upgrade” for VM, it is a creation of a new Generation 2 VM from the existing Generation 1 VM.
Be careful before you proceed with transformation and read all the documentation!
The script can be downloaded here.