If the tag says it can be set to run from 115 volts you'll need to open the cover on the motor as well as change the plug. There should be a small plate on the motor that covers the electrical connections. Take the cover off. There should be a diagram there that gives the necessary wiring connections to covert the motor to 115 volts. Make sure you know what you're doing because you could damage the motor if you wire it incorrectly or even create a shock hazard. By changing the motor to run from 115 volts you'll also reduce the power of the motor. You can't run a 3 horsepower motor from a 115 volt circuit. It needs more current to have 3 hp than a standard 115 volt circuit can deliver.

Buy an Automatic Voltage Regulator (AVR) which can be found in any department and hardware store. If your country runs on 230 volts, then I don't think you need to convert to a 115. But if your country runs on 115 volts, I strongly urge you to buy the AVR because if you run a 230 volt machine in an outlet that only supplies 115, you could damage the machine.