There are two ways to change the order.
First Method:
This method don't need any programing skill
1. Remove all navigation items from Admin > Pages and uncheck all pages checkboxes. This will remove all links (if you don't have any additional link or page)
2. Now go down to the page and find Add Link - click on that it will ask to add
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Text of Link: Here you can set the Menu label
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Position: You can select the position you want
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Visibility: To the user you allow to see the menu
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URL of Link: Here you add the URL of the page
Example:
Lets say you wan to move Ask a Question at the first than
So for this just copy all pages url before you remove from the menu and use it as I mention above
Second Method
This will required some programing skill or at lest know how to modify the code
You can follow NoahY's technique to modify your Menu without removing pages or adding new links
http://www.question2answer.org/qa/6979/how-can-you-change-order-of-navigation-items?show=12966#a12966
Get code from above link and add to your theme's qa-theme.php file