For various reasons you might want to manually change your MAC address for your network card.
There’s an easy way that you just need to edit /etc/network/interfaces file on your ubuntu.
Run following command in terminal
sudo gedit /etc/network/interfaces
File will be opened up,add this line at the end.Close and save it.
hwaddress ether 01:02:03:04:05:06
Change the address to what you want,the random number is hex.
At last restart networking:
sudo /etc/init.d/networking restart