How do i stop my computer from asking me to change my pword every month?

I have a dell optiplex pc given to me from a school. Unfortunately upon making my own account I deleted all of the other accounts. Including the system admin one, however it still asks me to change my pword every month, I have checked for software on the computer that would do this and there is none, so it must have been in the settings in the account i deleted. Is there any way I can stop it asking me to change my pword without the sys. admin account?