On my breadboard with a serial lcd display ive just got a toggle switch on flying leads on the 5v feed to the serial interface.
When I upload a sketch to the Arduino I just flip it off and when it finishes I flip it back on.
You may want to then reset the board to refresh anything you display on the lcd if your sketch doesnt update the lcd very much like my sketch.
You could replace the switch with a relay. if you realy need to.
There are plenty of examples on using relays with the arduino if you search on google.
Gordon