There are two different ways to change the URL of your Facebook page depending on whether it is a profile (for personal) or page (for businesses).
How to change your Facebook URL for a profile
Head to your Settings & Privacy that’s located in the top right of your Facebook page under the drop down menu
Then click on Settings in the next menu
In General Account Settings click on the pencil next to the field that displays your Facebook URL
Enter a new Username, and make sure your new username is available.
Once you’ve entered an available username, click Save Changes
How to change the Facebook URL for a page
You must be logged into the admin account linked to your business page to do this.
Head to your Facebook business page and click on the About section
Click on Edit Page Info in your About section
Enter the new name into the Username field
This will automatically save your changes once you click outside the Username field if the new name is available