The specifications of the MSP5 imply that it has a "universal" power supply that will run on US or European mains voltages, so all you should need do is change the plug (or use an adaptor). However, the manual also says that the operating voltage is stamped on a plate attached to the rear of the monitor. It would be safest to check with Yamaha, otherwise it could be expensive.

My pair is marked 230V 50Hz (I live in Europe), no switches visible from the outside. There might be different versions but do check with Yamaha.

Gunnar