Some classmates have changed their e-mail addresses (bad ones bounced back). Can I change their profile e-mail address or do they have to log in using the old one and change it themselves?

Very good question Julie, and I'm glad you asked it, because this is a very important issue.

The answer is that both of you can change the primary email address. If your Classmate logs in and changes it, it's no big deal. But if you do it, then it's imperative you inform the Classmate you've done this. Otherwise the Classmate will no longer be able to log in. If you change a Classmate's email address on his or her behalf, always email the Classmate and explain you've made the change, or give the Classmate a call so the individual does not get locked out of the site.

Thanks for this info - how does it affect their password if I were to change their e-mail address? If I change the e-mail address, is that their new login and does their password remain the same?

That's exactly right. If you change the email address, that becomes the new login, and it does not have any impact on the password.