Reversing a power supply with an spdt switch?
You can use a dual supply, use the switch to control the motor and a half bridge, or use the switch to control a SPDT relay (or a full H bridge/DPDT relay but in the latter two cases you only need a SPST switch so you are 'wasting' one contact on the switch and replacing it with another contact or transistor(s)). 



If you have two supplies (eg. a bench supply with +/- outputs) - not likely:







simulate this circuit &ndash; Schematic created using CircuitLab



More likely situation (only one supply available): 







simulate this circuit

Since SPDT relays are much cheaper and more available than DPDT relays (eg. JS1a type) this would be a better solution if your switch can handle the motor current (and a bit more for the relay). 

If you want to add suppression to the motor to minimize contact arcing, connect a bridge rectifier with the 'AC input' terminals across the motor, and the + terminal to the positive supply and the - terminal to ground, as shown above.