Windows XP Professional Help

Hi Everyone,
So, my mother has this computer that she used in her work and it has Windows XP Professional. She quit the job and she wanted me to remove all the security stuff they put in it in her work. This is just a little back story.
The problem is:
They had 3 admin accounts. For some stupid reason, I decided to make all of them standard account. I did it and now I can’t do any changes in the computer’s settings. I can’t even go to the user accounts place. Also, for security reasons, the IT people in her work put something that won’t let me access any usb devices.
I just want to restore the computer so that I can update to the newest windows version. Could you please help me?