I did this for a lower end FPGA board of theirs.
It was for the free version (Diamond 3.9 64 bit), which they seem to insist is LOCKED to my Ethernet's id number (MAC address), so I used the automated thing (on their website and by supplying my MAC address) to get the licence file emailed to me, put it in the right place, and it seems to be working fine now.
Having to first register on their website was also a nuisance, which had warnings that filling it out wrong in some place(s) would mess things up. But fortunately I seemed to do it correctly.
I've NOT needed to contact their support (yet).