Removing/ Replacing Administrator On 8.1

I purchased a used computer that had 3 users listed with one being the administrator. I have the password for the current admin. I removed the two users and want to change the admin to myself or for that matter, I don't necessarily need an admin (unless 8.1 requires one) as I will be the only one using the computer.

So do I even have to have an admin? If not, how do I rid the one I have?

And if I have to have an admin, how do I change the administrator to myself and delete the old/current admin?

Thanks In Advance!!

 

Windows needs one Administrator account.
You first have to create a new Administrator account for yourself, and then you can delete the other admin account.