First of all you have to open Terminal
Type the following command to check the mac:
1. ifconfig -a | grep HWaddr
(Note it down somewhere )
2. ifconfig eth0 down
ifconfig eth0 hw ether 00:70:5D:34:54:02
(Any mac address you want to give)
ifconfig eth0 up
ifconfig -a | grep HWaddr
(To check your new mac address)
Note:
1. mac address should be in hex dec.
2. you can change mac add. of any interface
but you have to specify name