Lift up the battery cover under the seat.
Loosen the hook-and-loop straps holding each battery in place.
Pull apart the wiring connectors for each battery by hand.
Lift each battery straight up and remove them from the battery compartment.
Remove the wiring harness leads from the battery terminals with a Phillips screwdriver. Attach the harness to the replacement battery, ensuring that the red lead is attached to the positive battery terminal and the black lead is attached to the negative battery terminal. Tighten the wiring harness leads with a Phillips screwdriver. Repeat for the remaining battery.
Lift each battery up and lower them into the battery compartment. Tighten the straps over the top of each battery to secure them into position. Plug the wiring harness leads back into the wiring plugs in the battery compartment until they are fully seated.
Close the battery compartment cover.