You can only change the password registered on Deskree if you signed up for Deskree using an email and a password. If you authenticated using OAUTH, you will not be able to change your email or password.
If you registered for Deskree using an email and not using OAUTH, click on the small arrow beside your profile avatar:
click on account settings:
Here you will see the option to edit your password:
To edit your password, you will need to enter your new password and your current password.
Be sure to click "Save".