Hi!
I have done "normal" licence upgrades but not this particular CPU-D5C to CPU-D5 upgrade, but the process is the same; you download the "ULK file" from your system, buy an upgrade licens which is delivered to as an UPN code. Then on the license web site you upload your ULK file and from the UPN code you can download a new licence file, which then is transfered to the licence carrier board in your system (in this case your CPU-D5 board and the Compact Flash).