How do you install windlws xp ?

Question

how do i wip my pc clean and install a new xp on it i bought the pc and it has a passwoed the owner does not have any more so i have windows xp the same that is on the pc i tried to install it but it wrote over the xp on it and stll askes me fro the old password so how do i wipe my pc free and install the new xp