I will need to investigate this as well as I don't have a good answer for you. In the meantime, if I were you, I would logout of Pega Community. I wouldl click the Login link and from that page I would click the link Forgot Password. Enter your email address and submit the request. You should receive an email allowing you to reset your password.
Sorry, guess I shouldn't answer questions late at night :) I was not able to see the option to update my password as we use our Pega network password to login to Pega Community. I was however able to update my password using a different email address I have registered with Pega Community. To do this I followed these steps:
1. Click the Hello <Name> link in the upper right hand corner of any Pega Community page and select My Profile.
2. Under your profile picture click the Edit profile link.
3. On the right column at the bottom you fill find a Password Reset heading. Here you will be able to reset your password.