You can only change (edit) your yt username ONCE, then you can never change it again. So, you only have one time to get it right, and they do NOT make it obvious how to do that (like they used to).
Here's how to locate that spot...
after you create your acct. go to you tube, and go to this page...
then look to the LOWER LEFT, and you'll see this in TINY writing!!...
Would you like to appear on YouTube as a different name, brand or organization?
Create a username <----(((click on this)))
Hope that helps!