The account is created in previous Windows versions, but since it’s not enabled you can’t use it or even see it.

The Administrator is a hidden elevated administrator account that has full unrestricted access rights and permission on the computer. By default, this elevated “Administrator” account is not prompted by UAC by default to provide confirmation before allowed to make any changes that require elevated administrator permissions since it is an elevated account.

Note:
It is recommended that you create and use your own account with admin privileges.
If you enable the built-in Administrator account, then it is recommended to create a password for better security.

Step 1. Right click on Start, then choose “Command Prompt (Admin)“. (or Win + R)

built-in-admin-step1

 

Step 2. You will be prompt by the UAC, click Yes to allow the app.

built-in-admin-step2

 

Step 3. On the Command Prompt type “net user administrator /active:yes” and press Enter to run it.

built-in-admin-step3

So, you will probably be prompt with this message; “This app can’t be opened using the built-in administrator account. Sign in with a different account and try again.” Follow the next steps so you can continue using the Windows Administrator account as you please.

built-in-admin-step5-0

 

Step 4Click on Start and type “Local Security Policy“.

built-in-admin-step3-2

 

Step 5. Go to “Security Options” under “Local Policies“, find “User Account Control: Admin Approval Mode for the Built-in Administrator account“, right click and Properties.

built-in-admin-step5

Step 6. Select Enabled and click OK. You can close the Local Security Policy windows using the X on the right corner top.

built-in-admin-step6

Enjoy!

Source: http://goo.gl/wdtn09