How can I change 110 volts AC to 220 volts AC

Yes. But lets find out why you want to change 120 to 220.

You would need a step up transformer. What do you need the conversion for (i.e. appliance, television, etc)? The reason I ask is that a hairdryer will require a whole different type than home electronics.

Here's one suggestion, but a quick Google will result in many responses.

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Thanks for the respond I need it for Hairdryer in the Bath room

Oh that's easy. Most large department stores or electronics stores will carry it in the travel section.

Thanks Gregisteedtrademark