You need to install these applications:
sudo apt-get install xbindkeys xautomation xev
Use "xev" to find the button number that you need. You will see a little white windows appear, put your mouse in it and press the button.
You should get output like this for each button:
KeyRelease event, serial 41, synthetic NO, window 0x4e00001,
root 0xc6, subw 0x4e00002, time 430656, (39,24), root:(765,76),
state 0x10, keycode 38 (keysym 0x61, a), same_screen YES,
XLookupString gives 1 bytes: (61) "a"
XFilterEvent returns: False
KeyPress event, serial 41, synthetic NO, window 0x4e00001,
root 0xc6, subw 0x4e00002, time 432854, (39,24), root:(765,76),
state 0x10, keycode 56 (keysym 0x62, b), same_screen YES,
XLookupString gives 1 bytes: (62) "b"
XmbLookupString gives 1 bytes: (62) "b"
XFilterEvent returns: False
The important lines are the thirds.
Now create the xbindkeys config file using:
xbindkeys --defaults > $HOME/.xbindkeysrc
Inside this file you can change behavior of all keys or combination of them.
gedit $HOME/.xbindkeysrc
Now you need to restart the pc.