The easiest (and most recommended) way is to find the reset jumper. Sometimes it's right by the CMOS battery, but it's often grouped with other jumpers to make it easier to find. Look closely for a 3 pin set that has a jumper on 2 of the pins now (this can sometimes be a DIP switch also, but those are more rare). It is typically labeled on the board, but the label can vary: CLEAR, CLEAR CMOS, CLR, PASSWORD, PWD, etc. It should have a label that indicates something about clearing, passwords, or CMOS. If you find the jumper, be sure the power is off, and switch the jumper to the other possible location on the 3 pins. Note that some power supply & motherboard combos keep power to the board, so you may want to physically unplug the power, just to be sure it's off completely. Once the jumper is in the new position, power up, and the password should be cleared. If you know it cleared, shut back down, power off, and switch the jumper back to original position.
If you can't find the reset, try the battery again. However, be sure you are completely disconnecting power (not just shutting it off) when you pull the battery. Wait at least 5 minutes, then put the battery back in and power up.
If neither of those work, I'm not sure what to tell you. It's obviously not in EMachines' knowledge base, and the fact that there are no manuals available for download, and you have to pay for any support no matter what (with no option to just ask a question in a support forum or something like that) is a little annoying. Kinda makes their "CustomerCare" moniker an oxymoron, I think.
Good luck!