I am trying to know from firebug, am I able to know the location where I am able to edit the text for "HOW TO MEASURE"?
No, Firebug can't tell you that. It only looks at the HTML and CSS as delivered to the browser. The HTML of the page is (presumably) constructed from various files by something like PHP, but Firebug knows nothing about that.
Perhaps look in your actual template files on the server. That should indicate where the measurement code is coming from. It will be pulled in in some way, via an include or something like that.