Resetting Password

Have had a few attacks on my computer today (from Russia/St. Petersburg, according to the IP?). So, decided to reset some of my passwords. Can't do that in  this NIS Forum. Using my notes from a few years ago I enter what I thought was my current password, in order to change to a new password. NIS won't accept the password I thought I had. And, no way to find out what it is.  So..how do I change my password??

 

Tks for any help.