Lenovo Chromebook 11
Opening the case might void your warranty. It is also not recommended, since opening the case lifts the heat sink off the CPU and upon closing the case the thermal resistance might not fully recover. Especially, it is not recommended to run the device with the case opened.
But if you must open the case: Remove 10 screws (four of them hidden under the rubber feet) and then pry open the case at the seam.