Administrator Password Problems

I am trying to use my sisters old Acer Aspire 5050-3371 laptop, but she can't remember her password, what do I do?
i had created a new user account and deleted the existing user account.now i can use the new user account.but if i want to use dvd writer or internet it is asking to seek permission from the administrator.when i want to login as an administrator it is asking password.is there any solution to change the password of administrator so that i can use dvd writer and internet