|If this is a desktop computer, you can remove all passwords either by moving a jumper on pins on the mboard to the clear cmos position for a short time (e.g. 5 minutes) then moving it back (the jumper is often close to the mboard battery), or you can remove the mboard battery for a short time, then install it again (make sure you replace it so it's polarity is correct - look before you remove it - usually + is on the top side. Some mboards have a separate jumper that can be moved to clear just the passwords in that same area on the mboard, but that is not common.|
In either case you are supposed to remove the AC power to your case/power supply while doing so (that shortens the time you have to wait).
If this is a laptop, removing the cmos battery will not remove the passwords unless it is an ancient laptop (at least ~ten years old), or you may be able to use a procedure to remove the passwords if the laptop is old enough (at least ~5 years old), but otherwise the password(s) is(are) stored on a separate flash chip (not on the bios chip)on the mboard that cannot be erased by removing the power to it. If you are the original owner of the laptop and can prove that to the manufacturer's satisfaction (e.g. by providing info on the original bill of sale) you can often contact the manufacturer and they will provide information as to how to remove the password e.g. sometimes by using a special master password.
Otherwise, there are freeware utilities such as killcmos you can try but they often are of no help with newer laptops, or there are various master passwords you can try, but you're often only give a small number of chances, e.g. 3, to try a password, then you must reboot to try again, or you may need to send or take the laptop to a professional service such as a data recovery service to have them remove the password(s).