Personally, I wouldn't do it that way, I'd just do a backup and then restore it after I changed the battery. Fiddling around inside with the power on is just dangerous. However, if you simply must, then:
Back up the DM1000 to your computer or an SM card.
Power off and open up the DM1000
Find the battery
Power on the DM1000 and replace the battery after it boots up, being extremely careful not to short anything out.
After the new battery is in, power off the DM1000 and reassemble.