You cannot permanently change the document on the server.
You may, however, edit the html document you have requested.
- Save the file, and edit the html source with a program like notepad. You may change the button's like.
- You may use the Inspect element tool in your web browser to change the like. Right click the page: Inspect Element (for Firefox and Chrome). Some other browsers like IE or Safari, look in the menus for web development.
Remember you can't permanently change content on some else's page, you only have requested a copy of it. This copy which you can edit.