You can reset passwords for users if you have administrative authority. You want to get to the Collective level and towards the very bottom one on the menu items is information about users. This will give you a list of all the collective users. Then click on the user name in question and it will allow you to enter a new password for that user. Sorry I can't remember the exact menue sequence to get there but just keep looking; it's there.
I found this today as I discovered that some of my users were issued different usernames when they were invited to join subsites. Then they entered alternate passwords and got all screwed up. The advantage of using the Collective list is that this list shows all users of all sites associated with the collection of sites.