Required Things :-
1. Facebook Account ( Username Changed up by one or Two Times )2. Facebook Page ( Which is above of 25+ Likes )
Must Follow the below Steps to change you Account's Username
1. Login with your Facebook Account where you want to change the Username after the Limit.
2. Now Open your Facebook Page which is of above 25+ Likes
3. Now Click on the Edit Page which is on Top Centre in Admin Roles2. Now Open your Facebook Page which is of above 25+ Likes
4. Menu will appear below, Now you have to Click on Update Page Info
5. Now New Page is Opened, Click on the Facebook Page Address
6. and Now Change Web Address
7. New box will be appeared, Select your Page and Enter the Same Web Address which is of you Facebook Account.
for example :- My Account's username is www.facebook.com/iAnmoldeep So I've to Paste Same Web Address in the Change web Address Box
8. Now you'll see that Facebook Shows the option - Transfer Username Click on That and Save.
9. You'll See that your Account's username will be Transferred to your Facebook Page.
10. Now Click on Settings -> Username
11. Last is your have to Set your Suitable New Username Which is avaliable, then fill the Password and Save It.
Enjoy !! New Username is Setup on your Facebook's Account