Unscrew the 2 Phillips #0 screws from the back plate of the calculator.
The screws do not come all the way out. Simply twist them until you are able to remove the back plate.
Remove the back plate using the spudger or by hand.
Carefully disconnect and remove the old battery.
Unhook the wire from the tab.
Carefully pull out the wire.
Grip the wire close to the top and pull away.
Plug in the new battery.
Make sure to put the wire back in the same way. You should see 4 metal connections on top
Position the new battery and tuck the wire under the tab.
Replace the back plate and the 2 screws.