Editing Shopify home page menu bar and tab slider

We want the freelancer to align the home page to the margins of the website. We would like to modify to menu bar megamenu. Our shopify website is [login to view URL] We want to menu bar to go down like www.xenonhids.com. Ours opens by having a background of full width. We want to adjust it to the amount of items in the menu dropdown. We also want to chose the products to put in the dropdown. Now we can only put 1, we want to put several ones. Thanks