Updating the User Information List Item with Web service is not working in sharepoint 2007

Question

i am trying to update the user details in User Information List using web service.

Web service is showing operation completed successfully and there is no error. Still the item value is not updated.

below is the update xml for web service

        <Batch>
            <Method ID="1" Cmd="Update">
                <Field Name="ID"><Entered item id here></Field>
                <Field Name="UserName"><Entered usename here></Field>
            </Method>
        </Batch>

Response is returning above item with details without any error.

Cant we Update the User information List using Web Service?