How do I rename a page if I get the title wrong?
You can't. You have to:
1. Create a page with a better name, perhaps using the Page Creation Form.
2. Drag the contents of your original page to the new page.
3. Look in the page Journal. Search for all the pages that refer to the old name (putting the page name in the search field at the bottom), then edit them to use the new name.
You can at this point Delete Page. However, if other sites are likely to have links to the old name, you may instead retain it with only a link to the now page.