Changing your password is done in the Settings > Security section of your YTMonster account. This section can also be found by hovering your avatar in the upper right corner of the website and then selecting Settings from the drop-down.

In this section, you must enter your current password and your new password (the one you want) in their respective fields. Finalize it by pressing the Change button.
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Once done you will be notified of a successful password change.