When you create a Page in Facebook, a random URL generates by the system to your page that looks something like this:
When 25 or more users have “liked” your Page in Facebook, you can use an easy-to-remember username (or vanity URL) for your Page that may looks like this:
Once you have claimed the URL (or username) for your Facebook Page, there was no option to change it. The only workaround was that you delete the old Facebook page (thus losing all the likes) and recreate a new one with the desired username (provided it is available).
Well that old policy seems to have changed recently and Facebook Page owners can now change the usernames of Pages that they are admin of. To get start, Open any of your Facebook Pages, go to Edit Page – > Update Info and click the “Change Username” link under the Username option.