You can't, you have to install a separate 240 volt circuit breaker and run a new 240 volt cable of the correct size from the breaker box or fuse box panel to the location where you want to use the 240 volt appliance.
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By asking this question you probably aren't quite ready to take on this particular task.
That you asked this question here shows that you don't already know your local Wiring Codes or Regulations so don't know how to calculate the correct wire size to use for the length of run from circuit breaker to power outlet.
Really, don't do this one yourself. Electricity is far too dangerous to handle if you don't already know your local Wiring Codes or Regulations or you have not been trained how to do this work.
For your safety - and that of anyone else who may use the 240 volt appliance - ask a professional licensed electrician to advise you or to do the work for you.
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How to do this job depends entirely on the Wiring Codes or Regulations for the locality (Town/State) and on the exact location of the appliance you wish to hook up: if it is in any place subject to water splashes or spray - such as in any room supplied with running water pipes, like a kitchen, bathroom, shower room, etc., or in a pool-side area - the codes specify that special precautions must be taken.
Depending on where your home is, it may be illegal to attempt to do this kind of work unless you are already a licensed electrician.
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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.