Can't install WordPress "not_found"

I have just uploaded WordPress 3.5.1 to my FTP account. No file errors noted, but I’m getting an error message when I try to connect to my domain site.

I saved WP to https://www.thatboulderagency.com/here
I’m only seeing a 404 error code when I try to access it.

I read in the other forum that simply renaming the “htaccess” file might solve the problem. I accessed file manager in my cpanel and tried it, but nothing seemed to happen.

I truly AM over my head, I get it. But any ideas, I’d really appreciate — thanks!