Replace Tags in a Asp Page

Hi, I have  some asp pages where some tags need to be replace i.e the tag will look like the following 

<div id="div1"  attr="new"></div>
<div id="div2"  attr="set"></div>
<div id="div1"  attr="new"></div>

now i want to find the id's of divs which has attr="new" . and also i should replace attr="new" to attr="lazynew".  I should do this is as application i.e i will give the path of asp page then  the file should be taken and the above should be done automatically . Please Help me to solve this