As mention above, disconnect power, turn off the converter circuit breaker.
TAKE PICTURES !!!
Also mentioned above batteries are heavy. Help would make it easier.
Tools: adjustable wrench (2 if necessary). Flat head (straight slot) screw driver, to pry with.
Disconnect the black negative cable first.
Then the red positive cable.
I tuck the cables back out of the way so they don't touch anything.
Lift the battery out.
Make sure you get a DEEP CYCLE battery.
While at the store, have the guys mark the positive and negative posts with a white sharpie. Makes it easier to see when working in a dark battery compartment.
When you install the new battery be VERY careful to be sure the positive and negative cables go to the correct post. If not, even for an instant, it will blow the reverse polarity protection fuses in the converter to protect the converter.
Good luck