This article will help you to understand how to set Text and NavigateURL property of hyperlink control.
This is bit easy on server site but when you need to do on client side then you need to set proper properties to work in all the browsers.
var hyp = document.getElementById('<%= Hyp.ClientID %>');
Once you get the control on client side all you need to set innerHTML and href property of hyperlink control. Both innerHTML and href are synonyms of Text and NavigateURL property on client side.
hyp.innerHTML = 'New Text';
hyp.href = 'http://www.dotnetspark.com'
To set the text from client side set innerHTML and to set the navigate url set the href property of object.
This both property works in IE8,Firefox and safari.