There is no way to automatically convert old html text/image/video files to the CSP branded html templates. That means that each file must be "rebuilt" within the course by copying and pasting. Begin by clicking on the course content you'd like to transfer to an html template:
Next, highlight the content and copy it to your clipboard (Ctrl+c), then click the "Create New" button:
Next click "Page"
Next click on the "Select Template" dropdown, then one of the templates:
Click the "Fullscreen" arrows at the top right of the html editor:
Highlight the sample text and then paste your content using (Ctrl+v) or (Ctrl+Shift+v) to paste without formatting (this breaks any hyperlinks or quicklinks in the text).
Click the "Fullscreen" arrows again, then the blue "Save and Close" button.
Finally, delete or hide the old content from student view.