How to simplify xml request and response structure in .net web service

I want to simplify my web service request and response xml structure:

At present :

<?xml version="1.0" encoding="utf-8"?>
<soap12:Envelope xmlns:xsi="http://ift.tt/ra1lAU" xmlns:xsd="http://ift.tt/tphNwY" xmlns:soap12="http://ift.tt/18hkEkn">
  <soap12:Body>
    <GetAddressForPostcode xmlns="http://ift.tt/1K2cprr">
      <postcode>string</postcode>
      <addressline1>string</addressline1>
      <SearchType>string</SearchType>
    </GetAddressForPostcode>
  </soap12:Body>
</soap12:Envelope>

I WANT :

<GetAddressAuthorisation>
  <MethodParameters>
    <Postcode>SW14 7RD<Postcode>
 </MethodParameters>
</GetAddressAuthorisation>

Thanks,