So in your merchant panel navigate to Configuration > Design > Signup page theme.
Select which theme you want to use (Set as default), save and then simply click the Edit theme button. A dialog will open, but changing the content of any of those fields isn't necessary, just click Yes. This will automatically create a copy of this default theme.
Ok, now you have to set this freshly created theme as default. Then you can start editing it. Click the Edit theme button and wait for the files to be loaded in a new window. Generally, you have some sort of ftp access to all of the files, which you need to edit in order to change the content of mini-site pages. You can use our previous online help in order to understand how our template system works and how to find the correct files for editing
Basically, you need to find and edit:
index.stpl - if you want to edit Overview page
faq_public.stpl - if you want to edit FAQ page
tour.stpl - if you want to edit Tour page
footer.stpl - if you want to edit the footer in wide theme
Click save to perform changes and review your mini-site for results.