Headers and Footers Shortcuts
Word includes a very easy-to-use shortcut that allows you to jump right to the header: Alt+V, H. (Press the Alt and V key at the same time, then press H. You can continue holding down the Alt key as you press H or not, it is up to you.) A helpful mnemonic for this shortcut is "Alt View Headers," and it works great.
Once you are in the header area, you can then use the Down Arrow to move to the footer area and use the Up Arrow to move back to the header area.
Getting back to the main document using the keyboard requires a different shortcut key: Shift+Alt+C. This closes the header and footer areas completely and returns you to where you were in the document.