How do I use the move to function to rename an article?

Make sure you are logged in. Only logged in users can move articles. Then just pick the "Move" button at the top of the article, and type in a new article name, and type a reason for the move.

It is also a good idea to use the "What links here" button to find any pages that link to the old article name and update them to point directly to the new article name (although this step is not essential, since moving an article automatically creates a redirect from the old article name)