Hi Ifthekar.
Kindly follow the steps
1. On your current exiting system you have to upgrade the support package stack level 26 with Kernel 7.21 Ext to support the Windows 2012 R2/ DB- Ms Sql 2012 R2.
2. On the new hardware you can install the Windows 2012 with MS Sql 2012 fresh.
3. Do the system copy from old to New H/W homogeneous system copy method. & Upgrade the SAP from ECC 6 SP 26 to Latest version ERP 6 EHP7
Regards
SS