When you first install WordPress, by default you’ll have an administrator account called “admin”. Admin is the username given along with a generated password to log into your account (dashboard).
This is great (actually needed) for setting up your new WordPress website/blog, but for security measures you need to change this simple login to something hackers can’t get by so easily.
If someone wants to gain access to your files, all they need to do is keep trying the username “admin” and endless password combinations (using automated programs), and eventually get in.
Don’t worry, it’s an easy fix!
Fortunately, you are the webmaster of your domain; that sounds pretty cool, heh! 
Step #1
When you are initially logged-in with the admin username, go to the User’s dropdown on the left side menu of your dashboard and choose “Add New”. Create a new user from this screen (all you need to fill in are the required fields for now). Make your new username hard for someone to guess, and of course, a strong password. Change the “Role” to Administrator and click Add New User to save your changes.
Step #2 is below this image and is VERY IMPORTANT (this is what gets everyone confused)!
Step #2
After creating a new user with your Role of Administrator, log out of the current Admin user and log back in with the new username and password. Go to the Users screen and delete the old “Admin” user. The trouble everyone has is trying to delete the admin user while currently logged in with that user; can’t do!
I previously had a post that goes hand-in-hand with this one that shows you how to remove the wordpress admin link in the footer of your website using Thesis.
