You can set a new password for an SFTP/SSH user as follows:
Select the desired project.
In the Website tab, click the subtab SFTP & SSH.
Click the three vertical dots next to the SFTP/SSH user you want to configure.
Click Set password.
Enter the chosen password in the Password field and then repeat it.
Click on Save changes.
The SFTP/SSH user's password has now been changed.