How to Change a BIOS Serial Number
Your BIOS serial is saved via software, not hardware. Like anything else that's software based, the BIOS serial can be changed. The serial number data, as well as date and time are kept running even when the computer is powered off through a tiny battery called the CMOS battery. By turning off the CMOS battery, you can force the motherboard to lose it's BIOS serial number data and automatically generate a random new number when its rebooted.
Things You'll Need
Turn off your computer and disconnect any power cables coming to the computer. Touch your hands on a metallic surface that's grounded to discharge any static electricity on your hands.
Unscrew the screws on the exterior of the computer and open the computer case. Look for the motherboard, which holds the CPU. Locate the CMOS battery, which looks like a coin roughly half an inch wide.
Pull up the clip that holds the battery in place. Lift out the battery. If there is no battery clip, use two fingers to pry the battery out. In either case, it should be relatively easy to get the battery out. Do not use excessive force.
Wait 30 seconds to make sure the power to the CMOS is completely drained.
Place the battery back into its socket.
Turn on the computer. Press "F1," "F2," "F12" or "Del" to enter setup mode. Your BIOS serial number should be changed. Note that you'll also lose data on additional drives to connect on startup, any custom BIOS settings, BIOS passwords as well as time and date. Change all the necessary settings, save your changes and reboot.