Remore the 15 screws with a Phillips Screwdriver.
Keeps the 15 screws.
Find the battery connector.
PS: Don't worry, those are all low voltages and very safe with no hurting.
Separate the connetor by hands (very tight, here is a skill, I spinned them inter-reversely very very little bit while pulling them out, or you may use a tool like tongs, as long as don't hurt the wires and connector).
Then disconnect the black connector(red and black wire, connecting to batter)
Loosen the 4 battery screws, and replace the new battery. Tighten 4 battery screws and plug the connectors correctly.
Testing the power button if it works properly.
Insert the 15 screws with a Phillips Screwdriver.