The absolutely best place on the planet to find out about stuff like this is the Joomla! forums. First hit in google for the search ‘How to remove Joomla because open source matters from header’ (no quotes in the search, of course) brings you to:
"1) Manage Templates (ja-purity), switch from Image to Text. Add your Site Name & tagline. Save
- Create an image ( 207px x 80px ) called logo.png. Rename original …/templates/ja-purity/images/logo.png, then replace with your new file. Recommend using background transparency rather than solid. Recommend Paint or Gimp creator/editor.
Upload using ftp client ( filezilla, etc ) or File Manager in your Cpanel."
–DreamHost Tech Support