Can´t upload new sketches to my ROBOT ARDUINO

Hi

First day with my robot arduino...

After uploading few sample sketches to my new toy, a robot arduino,, the last sketch (motor control) continues on the robot and I can´t upload new sketches. I´ve tried to reboot (double click on the reset button) and nothing... the sketch is still here... When I upload a new sketch from my PC, It seems to reboot correctly but what I get is the same sketch, motor control !!

Please, someone can help me?

Thanks in advance

JC