For anyone still interested. I know I wil be likely banned for this but this post is old and will probably not be checked.
First of all, remove the sticker on the back. Then remove the 2 screws near the UART port. Take off the top part of the M5StickC. You should see the board and the screen now. If your goal is to remove the screen, then just rip off the side that is closer to the edge and unsolder the connections on the other side of the screen. The screen should be off now. For people who want to change the battery or do other modifications you can take 2 paths from here. 1st path includes unsoldering some connections. 2nd path is safer, but looks sketchy. Anyways be careful since if you damage a line/wire, it can result in some features not working. I accidentally beheaded my home button while disassemblying my M5StickC.
1st path:
There are multiple little soldering points on the sides of the screen. Unsolder them and pull out the motherboard. Be careful, the battery is still attached.
2nd path:
Take off the GPIO pin cover. Pull it away from the main case (parallel to the longest side of the M5StickC). You should see multiple fork-like connectors now. After that you can take the board out.
And that should be everything. Everything else is straightforward. wanna change a butto? Unsolder it, resolder a new one. I am not helping you here. Good luck!