Your password defines your Birdee ID. By changing it, you need to change your login credentials and be disconnected from the application.
To change your password:
Log in to your customer area
Click on your user tab, on "My information"
Go to the sub-section "Access"
Click on the "Define a new password" button next to the password field
Complete your old password and enter your new password twice
Click on "Confirm"
You are disconnected from the application
Click on the "Login" button on the confirmation page of my password
Log in with your new credentials