Make sure you have planned out the changes you wish to make to the announcement you want to edit. Then follow these steps to edit the announcement:
Make sure you are logged into an account that has permission to edit announcements.
From the Control Panel, select the Site Content tab.
Find and select the Announcements module.
You will be shown a list of current announcements.
Locate the announcement you wish to edit and click the Edit button for it under the Actions column.
Make any changes that you had planned.
Take a moment to proof read your content and double check your settings.
Click Save to save your annoucement.