Change your FTP password by following these steps:
1) Login to your 1st Domains Account
2) Click on 'Manage Domains & Services'
3) Click on the domain name in the list
4) Click on 'Web Hosting Control Panel' to be logged into Plesk Control Panel
5) Under the 'Hosting & DNS' tab, click on 'Web Hosting Access' or 'Hosting'
6) If using the "Web Hosting Access" option. Under the System User enter or generate a new password. Click on Ok.
7) If using "Hosting Settings" scroll down the page and look for Webspace settings. Under there you will have a system user's credentials. And it is here that you generate or add a new password. Click Save at the bottom.
8) Make sure you note that down as you will need that password to use with your FTP client.
Important: Make sure your FTP password is strong. So, use capital letters, numbers and special characters throughout the password. Using the generator will generate a strong password for you.