How to I change the voltage from USA specs to UK specs?

I need to change it from 120 to 230 so it does't blow up when I plug it in.

On the G4 tower, the switch is right at the back. Unable to locate switch on the iMac.

Please help.

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Boy! I don't remember if this system was a dual voltage or not. If you look carefully near the plug socket you should see a marking telling you if it can support 120/220 volts, if is shows both then its a dual power supply. Maybe someone with a schematic can tell us for sure.

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