If you want to change your Firmhouse password, you can do so by:
Clicking on Profile Settings in the top right corner
Entering your current password, and the new password you want to turn it into
As such:
Note: your password has to be longer than 10 characters! If you cannot think of a good password or keep forgetting them, consider using a password manager like 1password (OSX / iOS now has a native password manager as well).