Unfortunately, the Codex is badly out of date. It repeatedly refers to Manage and Options menus that do not exist in 2.7.1, and so I have no idea what I can and cannot trust in it.
I know how to use FTP. What I'm asking is, where would I get the file to edit? I just came from Blogger, which has a very simple option to open up an editing window with the HTML for the entire site. On WP, I find links to Editors for the Theme files and the plug-ins, but nothing for the overall site.
The plugin you gave me worked just fine, but surely it should be possible to copy and paste a few lines of code into the HTML?