To change the mac address of your ethernet port follow the steps below.
Type the following in a terminal with root permission
1. Disable your ethernet.
# ifconfig eth0 down
2. Configure new mac address.
# ifconfig eth0 hw ether 1b:2a:4c:4d:8e:9f
(1b:2a:4c:4d:8e:9f is only for example..give your preffered mac address)
3. enable your ethernet
# ifconfig eth0 up
Check your new MAC address by using
# ifconfig