this page will show you how you can change the page title on the browser even after the page has finished loading you can change the title tag in html 
first look at the title of this page, it probably says: how to change page title on browser
now i am going to change it to: I Changed The Title Wallpaperama!!
ok, before you click on the link before, look at the top of the page the title of this page, then click and look at the title again and you will see it changed:to change it, click here
so here is the code i used:
<span onclick="document.title = 'I Changed The Title Wallpaperama';" style="color:blue;text-decoration:underline;">to change it, click here</span>