I would like a text or hyperlinklink to change when i enter value(s) in a textbox in asp.net

I would like a text or hyperlinklink to change when i enter value(s) in a
textbox in asp.net

A part of my code looks like this, a simple hyperlink to an image.
<a href="http://www.google.com"><img src="Logo.jpg" height= "120";
width="280"; /></a>
I would want it such that i can change the link as many times as i want
but only through a textbox in another form.