Different layout / themes on each page

[Timbow]

But when I get inside of Pages - Edit Page - PAGE OPTIONS and try to change the Page Template it shows only Default Template options. I mean, I cannot choose any other template that I created before.

any filename.php in the folder theme/themename should show up as a template in PAGE OPTIONS . Check the file is there, check it isn't capitalised (aboutus.PHP won't work!), and refresh the admin page in your browser.

If you go to 'Theme' then 'Edit Theme' the right hand drop-down should show you the list of files in the active theme folder so you can edit them. Is your template file there?