Intro: How to Disable / Delete the Administrator Account From Windows 7 Computers
First, open "All Programs" in the "Start Menu" and then click on "Accessories".
Look for "Command Prompt" and right click it, then select "Run as administrator"
Click on "Yes" if it asks you, Do you want the following program to make changes to your computer?
Once command prompt opens, type: net user administrator /active:no to disable the administrator account
net user administrator [/DELETE] to delete the administrator account
Once you've typed in one of the following, hit enter. If you did the process correctly, it should say "The command has completed successfully".