You can change your Mindjoy password from your account settings, as long as you know your current one.
Changing it
Click your name at the bottom of the sidebar and choose Settings. The settings pages are listed down the left: Account, Profile, Security settings, Email preferences, Accessibility, Agent preferences, Integrations, Classroom Sync and Billing.
Open Account. Enter your Current password, then the new one, and click Save.
If you cannot remember your current password, sign out and use the forgotten-password link on the sign-in page instead.