To rename an item you can open, click Edit, and change the title. But is there more to a title than meets the eye? Maybe.
An item created and given a title is like a lovely swan landing on the water, in that Plone will create an instant underlying mirror image of the name to glide along too. This reflection is called the "short name." It has the elements of the title, but all in lower case, with hyphens instead of spaces between the words. If you call a file "All About Us," Plone will give it the short name "all-about-us."
The short name is used to create the unique url leading to your page. When a title is changed, the short name needs to be changed too. If the two do not correspond, this can cause confusion in links and search functions later as your section grows. The best practice standard is that when you change the title of an item, change its short name at the same time.
But first, search the website for the current short name (say, "all-about-us.") This will tell you which pages contain internal links to the current short name. Make a note of these pages, and after changing the short name be sure to re-create those page links to lead to the new url!
To rename an item, go to the folder > Contents, then click the Rename button at the bottom.
This opens a Rename Item box. Enter your new title. Then, derive and enter the short name in the correct box, and save.