Administrator accounts on Windows xp

I have recently taken a used computer out of storage. This conputer was replaced with a new Emachine. The primary administrator for the Emachine is the same for the used pc. As I am the soul user of the used pc I would like to prevent any access to it by the Emachine administrator. How can I delete the old administrator account or is there a way for me to rename the account so that I am listed as the primary account administrator?