After 6 years the house battery developed a short in one cell. I decided to upgrade to a Lifeline AGM GPL-4DL. My build has a rear storage box so this setup might differ slightly from your build. Some pics and instructions if you want to attempt this yourself.
I recommend eye protection and heavy duty gloves in the event something goes wrong and you accidently ground the positive terminal. You won't get electrocuted but you could get severe burns. I would also recommend turning off the main and fused breakers.
The battery weighs about 125lbs so supporting it is essential. I bolted down a piece of plywood to a floor jack.
After supporting the battery remove the four bolts that hold the bracket. I lowered it about 1 inch and then secured the bracket to the floor jack using some super long zip ties.
Remove the battery cover (not shown). Disconnect the terminals and clean them up with a wire brush and some dissolved baking soda. I recommend taping up the ends of your wrenches to prevent them from grounding out on exposed metal. My build has a temperature sensor for the Blue Sky 2000e solar controller which should be attached to the negative terminal. Coat the terminals with some anti-corrosive gel or protectant. If the bracket is showing signs of rust clean it up and put a fresh coat of paint on it.
Sportsmobile had some vinyl shims between the battery and the bracket. I reused them. You will also need to tie the battery down to the eyelets, I used two zip ties. Some of you are frowning right now
but that's what SMB used and they lasted 6 years.
Ideal charging voltage for the Lifeline AGM batteries is from 14.2-14.4 volts. The solar controller was set to 14.0 volts. I readjusted it to charge at 14.3 volts. The dip switches were also wrong, switch 3 needs to be on and switch 4 should be off for AGM applications.
Blue Sky 2000e Solar Boost Manual