Mirror HDD in Server 2012

Hello guys,

I made a windows 2012 Data center R2 server for my business. I installed the OS on a 250GB HDD. Because of reliability issue I bought a new WD 1TB HDD. I want to Mirror my 250GB HDD to the new 1 TB HDD. 
I tried to mirror the HDD using disc management by converting Basic to dynamic drive. But coz of the size differents I am not able to mirror the HDD now.
Can some one please help me fix this...
I even created a complete backup of my server and restore it back, that didn't even work.

Please Help!!!

Thanks,

Emmanual