Frontpage:

To rename a page and update the navigation links, switch to the navigation view, using the icon on the left.  Click on the page you wish to change, then click again on the text label.  Do not double click as that will open the page for editing.  Delete the current name and type your new name.  The page name will now be updated in all your navigation links, if your template uses a theme, as most of them do.

Other:

You will need to update the hyperlinks in each of your pages.  Using search and replace is the best way to do this.