How do you replace a 120volt outlet to a 240volt?

Answer for USA, Canada and countries running a 60 Hz supply service.

As you asked this question here the best advice anyone should give you is to call a licensed electrician to install a new 120 Volt socket outlet for you.

He will use the correct size of wire for the 120 Volt appliance you want to use and connect it to the correct size of circuit breaker on the main panel and also a GFCI safety device to protect users from electrocution if the room is likely to be damp or have water spray or wet floors, walls or ceiling, such as a laundry room or a kitchen.

Then you would be able to use a 120 Volt appliance safely in the room in question.

The answer given just below here is highly dangerousadvice. The reason it would be dangerous to simply do what it says is that the circuit breakers on a 240 Volt circuit are big enough to protect a clothes dryer, a kitchen range, or whatever the 240 Volt receptacle was intended to supply.

Those breakers are way too big to protect a 120 Volt socket outlet, because, if any small appliance plugged into that socket outlet were to develop a fault, it could catch on fire - or electrocute somebody - and the circuit breaker would never trip to cut the supply of electricity!

Also, if the 120 Volt appliance takes a higher current than the old 240 Volt appliance, the wiring from the breakers to the wall box may be way too thin to carry the 120 Volt appliance's current safely and the wiring itself could catch on fire. That could easily cause a serious house fire.

Answer -- BUT THIS IS DANGEROUS SO DON'T DO THIS! --Just use one leg of the 220. Should be black, red, white, wires in the box. Depending on age of wiring, there may be green and bare wires also. Black, white, and green SHOULD give you power, neutral, and ground in that order, but check to make sure.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.