Some of these detectors can be like a puzzle box to get open so you can replace the battery.
I tried some research on your detector. It's made by Kidde, but apparantly is an old model, and I could not locate a manual.
I have to say, as I have many times on this venue, that some manufacturers recommend replacing smoke detectors afer 7 or so years. They're so cheap, I can't argue with them.
If you're handy with hand tools, it's not a difficult job. But many folks are reluctant to try. S'okay. Any electrician will be able to do the job in short order.
Smoke detectors are required vitually everywhere in new residential construction. Local electricians usually get this work. So plan on 65-75 bucks for an hour of labor, and about 15-20 each for the detectors