Renaming Updates is best used for regular, recurring Updates that are sent on a frequent basis.
Eg. you may want to create an Update called "Investor Update" that remains in your sidebar but has a specific subject line and title each time it is publish (e.g. June Investor Update).
To rename an Update click the 3 dot ellipses and select "Rename" from the Update you wish to change.
This will retitle the Update in your sidebar. You'll be able to rename the Update whenever you want as well as a customer title & subject line for each Update.