Most of us are quite content with the Navbar but it's always nice to be able to tweak it if the mood hits you, by either adding or removing buttons. For example, you might not use the Opportunity functionality and want to remove it from the Navbar.
Once you've added or removed an item from the Navbar you might want to either increase or reduce the amount of room devoted to the Navbar buttons. You'll notice a slider (the line with several dots on it) immediately above the Navbar buttons. You can drag the slider up or down to change the area that appears on the Navbar.
You might have noticed two other options on the Navbar's Configure button: Show Fewer Buttons and Add or Remove Buttons. Unfortunately these two options lack the flexibility of the Navbar options. The Show Fewer Buttons option removes a single button from the icon bar, starting with the Reports button. Although the removed items then appear to the left of the Configure button, they are very small and hard to identify.
The Add or Remove Buttons option lists all of the Navbar buttons; supposedly the ones that you're not currently using are "dimmed". However, because it's so hard to tell exactly which icons are dimmed, you'll probably find it much easier to use the Navbar Options button covered earlier.