Hi Good Morning every one..
This is my Html Code.

        <img src="http://imgs.zinio.com/magimages/500299032/2012/416238969_170.jpg" alt="Nov-12" title="Food Network Magazine"         class="cover">  
    <select  id="myselect">
        <option value="B">Business Card</option>
        <option value="C">Corporate Card</option>
        <option value="D">Type #</option>

consoder i have three different images ,if i choose Business Card option it will show default image,if i choose Corporate option it will show second image(i.e, first image is automatically replaced by 2nd image),if i choose Type # option,the previous imge is automatically replaced by 3rd imge.
please i need very urgent help..thanks in advance.

Look into the jQuery .change() method. You can attach it to a select element with something like this:

$( "#myselect" ).change(function() {
  // your code to run on a change event
  // in your case, getting the 'cover' element and changing its src