For what purpose do you wish to make changes to this bit?
Scraped from WIKI:
MAC addresses are most often assigned by the manufacturer of a network interface controller (NIC) and are stored in its hardware, such as the card's read-only memory or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be referred to as the burned-in address (BIA). It may also be known as an Ethernet hardware address (EHA), hardware address or physical address. This can be contrasted to a programmed address, where the host device issues commands to the NIC to use an arbitrary address.
Anything else would be considered hacking, and unless you can describe the application in which you are attempting to make changes to your PC environemnet, I am not certain we can help.
Please post back and let us know why you need to change your mac. Do you even understand how to make a hexidecimal number?
"If you can't soar with the eagles, then don't fly with the flock!" - Oliver Sykes; Bring Me The Horizon