Connecting Site to Notepad

I recently ran a markup validation on my site, http://www.eatingwithgrace.com, for the first time and found a lot of errors (Results: http://validator.w3.org/check?uri=www.eatingwithgrace.com&charset=%28detect+automatically%29&doctype=Inline&group=0).

I want to fix these errors, but I can’t find the errors using WordPress’s theme editor, which is usually how I edit my site. I downloaded Notepad ++ so that I could edit the source code through that, but I am unable to connect it to my site through the FTP plugin. I don’t know what to put in the username and password or the initial remote directory fields. I’ve only ever used Dreamweaver for editing html and no longer have the program.

Any help would be greatly appreciated.