How to change this?

I was wondering how to change the "fernzyboy10" because it was an old email that I used and I don't really like it now. Nor did I when I used the email address.

What you are showing there is your user account name. I would not advise changing it. Unless it's really bothering you in which case I'd advise creating a new user account with the new name you want. You might find that annoying too since you may be copying some files around and customizing your settings again. Whether I advise editing your user name really depends on your level of experience and your tolerance for things going terribly awry.

Chuck is correct as to the best method for most. It can be done, but not something to go messing around with lightly.

I would encourage you not to even think about it without a current backup.

Here is the kb article for it. Read it, understand it, before you start.

With all due respect, those instructions in the kb seem fairly simple for even a novice user. I don't see how it could go "terribly awry". Am I missing something?

With solid instructions in most cases you are okay but sometimes changing user accounts can have other implications, especially if you are in a networked environment and sharing resources. The KB article really only shows you how to resurrect your home folder with a new account name. It will not fix other issues you might run into later.