Changing the operating voltage of a motor is just a matter of switching a few wires around on the motor's terminal plate. By switching these wires, you change internal wiring for the run windings and the start windings from a parallel hook up for 115 volts to a series hook up for 230 volts. You should find the series and parallel connections on a diagram affixed to the inside of the terminal box cover. If you cannot, a Century AC motor wiring diagram for 115 or 230 volts can be found online. The wires are color coded, and the terminals are numbered.
Accessing the Terminal Cover
Before doing anything else, turn off the circuit breaker to the motor's branch circuit at the service panel. Tape the circuit breaker in the off position, then attach a note to the service panel informing others that you are working on the circuit. Turn off the circuit breaker as a safety precaution, even if the motor has an on-off switch. Someone could accidentally flip the on-off switch on while you are working on the motor. Remove the screws securing the terminal cover plate to the motor's rear end bell. The motor's rear end bell is the end of the motor opposite the shaft end. Loose screws have a way of disappearing, so screw them back in their holes for safe keeping. Once you have access to it, examine at the terminal board and locate the terminals marked #3 and #5.
Changing the Voltage
The next steps will depend on the voltage you're switching to. Connect the "Brown" motor lead to the #3 terminal for a 230-volt hookup and to the #5 terminal for a 115-volt hookup. Then connect the Brown motor lead to the terminal appropriate for the line voltage being used with the motor. Either a male/female push-on connector or a ring terminal secured to a terminal post by a nut connects the brown wire. Next, connect the red and black circuit wires to terminals #1 and #5 for a 230-volt connection. Alternatively, connect the "Black" and the "White" circuit wires to the #1 and #6 terminals for a 115-volt connection. It does not matter which circuit wire connects to which terminal.
Finishing the Voltage Change
With a 230-volt branch circuit, both wires are hot wires derived from separates phases at the service panel, one from "A"-phase, the other from "B"-phase. The "Black" wire is the "Hot" wire originating from either "A"- phase or "B"-phase at the service panel. The "White" wire is the circuit's "Neutral" or "Grounded" wire and connects to the panel's neutral bar. Once you've completed the switch, replace the terminal cover plate and turn the circuit breaker on.