CMOS battery problems / erroneous display

Hi,
Please help me on my CMOS display errors. I am having this error, CMOS checksum error – Defaults loaded Press F1 to continue or Del to enter setup Pressing F1 will continue opening my Windows XP desktop. Pressing Del will allow me to enter my BIOS settings. I am receiving a series of hangs and freezes and I cannot set the clock correctly. If I set the clock, it will automatically go back to previous year 2006. And will give me error on expired certificate. I want to know how to reset my CMOS battery, as this will be my first option to resolve the issue.
If this won’t work then maybe my CMOS battery needs a replacement. Please send me some help.
Thanks a lot.
