You can in-place Upgrade your Home Premium to Pro, which will reset activation. When you activate with the Pro Product Key, it will require a robocall to MS which exchanges a series of numbers that update the hardware signature assigned to the Pro license. Home Premium is then released for later use.
MS wants in-place Upgrades within Windows 7 to be done using Anytime Upgrades. However, there is a workaround to change versions within Windows 7 by changing two registry keys, tricking the installer into thinking it is doing an (always allowed) Repair Install on the same version.
Set a restore point, type Regedit in Start Search box, rightclick to Run as Admin, navigate to key shown at bottom below to make the exact changes shown:
Now run the DVD from Premium desktop, select Upgrade, remain connected to internet to get latest Updates/drivers into installer, and it should work as it has every time it has been tried here so far.