In Setup, there's 2 options to control the top Tabs and the Left Navigation menu.
Setup --> Setup Tabs (2nd option)
From here you can activate, deactivate, and reorder the tabs at the top of the screen. To activate a tab, highlight the name and use the add and remove buttons to move them to the left and right panels. The right panel is the active pane, and the left panel de-activates the tab. Use the up and down arrows on the right side to reorder the tabs. Simply click a tab name, then the up and down arrows to reorder.
Setup --> Setup Left Menu (2nd option under Personal User Settings)
This is where you can control the Left Menu -- and it works just like the Setup Tabs works. Click a menu item and add or remove -- moving the Left Menu option from the right (active) to the left (deactivated) panes. On the right pane, highlight a menu item and use the up and down arrows to reorder the items in the Left Menu.