Holy crap, this almost seems like more trouble than it’s worth but if you’re looking to convert your “old” HD DVDs to Blu-ray, Wired’s How-To Wiki has got you covered. You’ll need a fast Windows machine, an HD DVD drive, a Blu-ray burner, 30GB of hard drive space, money, and a bunch of software.
The basic process involves ripping an HD DVD to your hard drive first, then following a four-step transcoding/authoring process involving various different pieces of software, and finally burning the converted files to a Blu-ray disc.
The cost of the Blu-ray burner and some of the software alone could put you up over $500. Factor that, plus the time involved and you might be better off buying a Blu-ray player and keeping the HD DVD player hooked up. Or buy a hybrid player. Or go ahead and convert everything. That’s the manliest of all options, I guess.
Convert Your HD DVDs to Blu-Ray [Wired How-To Wiki]