This is a premium business/professional laptop that has very few issues, but one of them is the lack of memory upgrades.
1. Remove the bottom plate
The bottom panel of this device is held in place by 8 captive Phillips-head screws. After you undo them, remove the stylus from its tray and pry the panel with a plastic tool.
As far as the battery capacity goes, Lenovo has put a 51Wh unit inside of the Thinkpad X13 Yoga.
3. Memory and storage
Sadly, there is no option for memory upgrades, as all of the memory chips are soldered to the motherboard. That said, this model can be configured with 8 or 16GB of DDR4 RAM, working at 2666MHz. At least, there is the relief you can put a larger or faster SSD in the form of an M.2 PCIe x4 drive.