Now, remove the 2x Torx T5 screws at the bottom of the screen
You can now shift the screen slightly to expose the post holes that the screen case sits in. Put your screwdriver in one of these empty holes (not a hole that a screw was in) and that should give you just enough leverage to pop the PCB board off the back case connector
Done! Now you have access to the battery, you can replace it or replace the entire back case.
PLEASE NOTE that if you're planning to replace the entire back case, the new battery/connectors board may not line up with your existing main board. I think this is because the two boards were connected and then glued into the back case at the factory, for resistance to moisture. If it doesn't line up, you'll have to cut away all the glue with an Xacto knife, a very tedious process.
If you're just replacing the battery though, there's no change in the way things line up so you can ignore that warning.
Assembly is, as they say, the reverse of disassembly. When reconnecting the main board to the back case board, it's helpful to flip the screen forward and press down on the area covered by the barcode. Very little force should be required for the connector to pop into place.