I am in a very utter confusion about the default theme set to my Magento store. Please check the pictures above. The very first picture says that Amsport 5 is my default theme whereas the second picture says that I activated Amsport 2 as my store theme. Now I have this Megamenu which does not appear in the Amsport 2 theme homepage, rather when I activate Amsport 5, it appears there. Can somebody please explain to me how this works because I am quite a newbie to Magento and I can't find my way through it.
Your first picture does say that your "Parent Theme" (not default) theme is Amsport 5. It just means that in the first instance it will look for theme overrides in your activate theme and if they don't exist it will "fallback" to Amsport5. Amsport 5's parent theme is "Magento Blank".
Your second image confirms that your current activated theme is Amsport 2.
When you say the megamenu is not working what do you mean. Is it a module you are using?