Well, here's one of the simplest methods to change that Facebook Username you're no longer comfortable with

You won't be able to input a new username, however if your current username is one that you aren't ok with and you would prefer the default then this will certainly help you.

Instructional Video Here

Step 1: Copy Your Current Username

Log in to your Facebook account

Go to settings and select username

Step 2: Create a Facebook Page

If you don't already have one that you can use, you are going to have to create a new page.

This does not need to be anything specific.

Step 3: Proceed With the Steps

Add the information required for the page to be created and skip through any unnecessary steps.

You will delete this page after when you're through changing your profile username.

Step 4: Invite Friends

Invite at least 25 persons to like your new page.

Step 5: Change Your Page's Web Address

At this point it's best to have two browser tabs open - one with your Facebook Profile, the other with your Facebook Page

Go to settings on our Profile and select username
Copy the section of the URL that follows "facebook.com/"
Now go to your new Page, click on "about" and look for "Facebook Web Address"
Click "Edit" then click "Change Web Address"

Step 6: Transfer Profile URL

Almost there.

Replace the section of the URL that follows "facebook.com/" with what you copied
Check availability, Proceed with Transfer

After this you will realize that silly username you may have chosen some years ago for your profile that you thought was cool but now regretting, has been transferred to the new page you created.

Your Facebook profile will now have a default username/url.