Yes, you need new licenses. The EV1 licenses don't update themselves.
I've contacted EV1 and they're pretty an*l about it. They will not provide you with new keys if you ask them, I've had a server be down for two weeks because a Plesk upgrade gone bad.
So, no, you won't be able to simply upgrade to v7.5. I've tried, and it failed.
Furthermore, EV1 claims that selling servers is their core business, and that their business is NOT delivering software for these servers.
I've got it on file, and it seems like a -very- strange comment from a company that is supposed to be one of SW-Soft's 'elite partners'...