You can change the password at any moment by selecting the Settings menu and choosing Change password.
You will be asked to type your current password. Then press continue.
Type your new password.
There is an indicator that shows the password's strength in four levels: low, medium, high and very high.
You can only change the password from medium level on. Once you have typed the new password, press continue.
Type again your new password in order to confirm it. Press continue. If both passwords match, the password will be changed.