You can't just replace it. Here's what you should do.
Buy 2 (in case one dies, VERY good ides to get more than 1) DVD burner LDs from SenKat. Totally unused. Great price, cheaper than buying a DVD burner to rip apart.
Buy 1 or 2 Aixiz module from
www.mfgcn.com which is the website of Aixiz Lasers. They ship worldwide. You want the 650nm <5mw 12x30mm, $4.50 US + $2.50 US postage.
Buy one or two torches as a host. There are several good ones, including the Dorcy Metal Gear which are available online with a bit of searching. Most places ship worldwide for a couple $$ extra.
Buy some parts for a DIY driver circuit, available online, or you can get SenKat to send you the parts when you order your diodes.
There you have it! Read up on the guides in the experiments and mods section, to find some excellent guides on how to assemble all this.
Basically, take the old diode out of the aixiz module and discard. CAREFULLY put the new one in. Connect wires to it, build the driver board, connect diode and driver, carefully turn up the driver power while monitoring the current, find a good spot, then whack everything into a torch!
Please don't ask for more details here, just go read up on how to's.
P.S. I'm 15, in Australia, and I managed to do all this!