Let's say your page has a URL of "https://myaccount.fastercampaigns.com/december25" and you'd like to change the suffix "page1234" to read "christmas" instead. To do this, follow these steps:
Click on "Pages" from the left-hand navigation:
Click on the "Settings" icon for the page you wish to change.
Change the value of the "URL" field to the URL suffix you wish to use.