<a id="Main4" class="LeftMainMenu" href="ContactUs.aspx">Contact Us</a>
This will remove the href attribute:
$("#Main4").removeAttr("href")
Remember to do it on page load event like below:
$(function() {
$("#Main4").removeAttr("href")
});
Or if you just want to remove the value of href
then
$("#Main4").attr("href", "")
This will make
<a id="Main4" class="LeftMainMenu" href="">Contact Us</a>
DEMO:
$(function() {
$("#Main4").removeAttr("href")
});
<script type="text/javascript" src="http://code.jquery.com/jquery-1.11.0.js"></script>
<a id="Main4" class="LeftMainMenu" href="ContactUs.aspx">Contact Us</a>