sign in as the remaining administrator (the user that you will keep)
click my computer
click control panel
click administrative tools
click computer management
click local users and groups on the left hand side of the window
double click users folder
right click on the user you want to delete (administrator that you will delete)
Left click on delete
Are you sure you want to delete the user? click Yes
Restart the computer
Once a user has been deleted, creating an identical name will not bring it back, it's permanent.
There must be at least one administrator, an administrator cannot delete their own account.