It depends on if now how to solder or not. If so then its relatively easy to replace an ESC (electronic speed control)they are also rather inexpensive to. You just have to make sure that you buy the right one so its matched to the remaining ones on each motor. and there are two power wires that have to be soldered to the main board and 3 wires from the motor that get soldered to the 3 spots on the esc. and a plug. But they are thick wires and need to be soldered well so that you dont have any cold joints that could cause a wire to come lose while in flight.
