To reset your Duolingo password, go to the Duolingo website's password settings page. Type in your current password and then the new one you would like to change it to. Choose a unique password that you are not currently using on other websites or services. Remember to select the "SAVE CHANGES" button that appears once you finish typing your new password.
For Tinycards, please follow the same steps and change your password via your Duolingo account, or go to your Tinycards account settings. Duolingo, Duolingo for Schools, and Tinycards accounts are one, and your username and password is shared between those accounts.
If you forgot your current password, please follow these instructions.