most everything displayed by simple press is done via the sp theme you are using and a template file… just like wp does in themes…
so you need to find the template file you want to change and make the changes… Andy told you which template files to edit too… so assuming default, you would look in wp-content/sp-resources/forum-themes/default/templates for those files…
if you are not using the default theme, then just replace default with the theme name in that location…
we strongly recommend you make your own theme before editing the theme so you dont lose any changes… see: http://codex.simple-press.com/codex/themes/theme-basics/creating-a-theme/ for more on creating your own theme…
you can find more general information on themes at: http://codex.simple-press.com/codex/themes/