The battery that needs to be removed is the CMOS battery which is located on the motherboard of the laptop. You'll need to disassemble the laptop by removing the bottom case plate which should give you access to most of the motherboard. From there you'll hopefully be able to see the CMOS battery which looks like a large watch battery.
I wasn't able to find a detailed description of your specific model on what screws to remove to access the mobo but I did find a video of someone assembling one here
. You'll kind of have to watch it in reverse to see what screws he removes to get to the mobo but it shouldn't be to difficult. Just remember where you got the screws from for reassembly later.
When you find it take note of weather the positive or negative side is facing you, carefully remove it from the board, hold the power power button for a few seconds, and then replace the battery the way it was before. Screw the back plate on with at least one screw and try to power up the machine.
That should reset the BIOS to the factory default and remove the boot up password. That should solve the issue.