Arclite theme- organizing pages

I am using the Arclite theme.

On this theme, on the bottom of the header there is a navigation bar that includes links to all the parent pages that I’ve created, and child pages appear in drop-down menus.

However, it appears to me that the parent pages are automatically placed in alphabetical order from left to right, and child pages in alphabetical order from top to bottom. I would like to place my pages in an order that is different from alphabetical. In addition, I would like to have the option to select which pages are displayed (keeping some pages hidden).

How can I do this?