If you want to change your old FTP password, you can easily change/retrieve a new password through control panel.
1. Log in to your account in control panel.
2. From upper menu, click My Services.
3. Browse to the domain for which FTP details you want. Click the detail (rectangle) icon located on the domain.
In product details page under FTP Details heading you find text fields for new password .
Edit it with new password and click on update button to save it.