Sure. It's very easy and the batteries are inexpensive--just a couple of
dollars or so. Open the case and look for a little flat battery around the
size of a quarter. It's normally held in place by a clip. You can either
take it out and take it to the computer store, or copy down the info on
it.
Before you take it out, it's prudent to go into the BIOS setup program and
write down all the settings you see there. When the battery comes out, you
usually have 15 minutes or so before those settings are lost, but it's
good to have a record of them just in case. (For that reason, I prefer
copying down the info to take to the store, and removing the battery only
at the last minute).