It is necessary to change your ProtonMail password from time to time as it improves your protection. If you want to change your password, proceed by logging into your ProtonMail account. After logging into your account, go to settings by clicking on the gear button at the top right side of the screen, and open the account menu and settings. Then click on the ‘Security’ tab where you will be able to change the password for your account.
You will be required to first click on the current password box and accurately enter your existing password followed by a password of your choice.

When creating a new password, be sure to make it complex by mixing uppercase and lowercase letters, numbers, and symbols. ProtonMail encourages users to create a very strong and complex password and provides additional help such as a strength meter and recommendations to do so.
After this new password is entered, you need to type it again in order to avoid possible typing errors. Thereafter, make sure to submit the changes. It is best to log out of all sessions, then log in again using the new password so that the update applies to all devices that you use ProtonMail on.

Bear in mind that password-protected encrypted messages can be extremely burdensome. If you forget your new password, you won’t be able to recover any of these because, as you know by now, not even Tormail Inc. stores passwords or encryption keys, so remember not to forget. It is wise to do this periodically, and make it a habit to check this setting regularly.

More Info: https://www.resetprotonpassword.com/

More Info: https://www.resetprotonpassword.com/how-to-reset-my-password-for-protonmail/