You need to log in the seedbox via SSH, when you have done it, use the command:passwd
Then you are asked to give your old password, which is followed by a request for a new one. If you want to change the root password, you will be asked to provide the new password without having to provide the old one as well. Important! The password you will type cannot be seen. If you complete this successfully you will receive the message:
passwd: password updated successfully
Now you can use your new FTP/SSH password on your seedbox.