@coin @fell You remove the screws and remove the battery. I've had to remove the battery in a smartphone once or twice due to the screen freezing and the power button not working.
If you need a special screwdriver, or if the tablet/phone using pegs or tabs that can't be removed without breaking the device (and voiding the warranty), then you can take it to the Apple Store and tell them to use their "genius" tools to fix it.