To edit your website menu, go to the Website module -> Menu editor tab. Here you will see the available pages (hidden from participants) as well as the pages already in the menu (visible to participants).
You can simply drag and drop the pages to switch them from invisible to visible or re-order them. Make sure to click save once you're done.
Please note that form pages (e.g. registration form, cancellation form, thank you for registering page, etc.) are only available when they are connected to the appropriate event workflow automations.