While editing the site, click on the pencil icon to the right of the menu. Select 'Reorder Menu’.
You also have the ability to move pages to different positions on the menu
To move the position of a page, hover over the desired page item until the edit pencil appears. Click on the edit pencil and then, click Move.
A Move Page should display. Here you can see the current position of your page i.e. Main Menu, Position 3
Click the 'Position page under' drop down button to choose where you would like to position your page under.
Click the 'Position' drop down button to choose the position of your page
When finished, click the Move button to move the page.