AVHD's not merging with VHD .. on Server 2008R2

Hi,

I have Server 2008R2 as Hyper-V server serving 2 VM.

one of them has 3 VDD and all of them are now AVHD's . 2 generations

There is NO snapshot ...

I have shut down the VM ... and the AVHD's have NOT merged ... how can I force this ...

I saw somewhere that I should install Server 2012 ...

Any help is very much appreciated

Thanks

Sepp

Thanks Sepp