HINT: The ‘two black stickers’ are the ends of the two parallel adhesive strips which hold the battery in. There is no other adhesive holding the battery, so focus your attention on these regions when prying the battery out!
As mentioned in a comment on the previous step, you don’t actually need to remove the SIM/SD card reader at all.
If you peel back the copper foil from the opposite end of the device, you can sneak the battery out (and the new battery in) by just sliding the battery ribbon cable out from under the SIM/SD card reader.
