To Manage FTP Access, please follow these simple steps:-
Set up access to files of your websites over FTP protocol.
1) Login to Plesk control panel.
2) Click on "Websites & Domains Tab".
3) Click on "FTP Access"
4) Click on Create Additional FTP Account.
5) Enter Following detail as Marked in RED.
6) To Change FTP Username and Password, Click on FTP Username.
7) Enter new Username*, Password, Confirm Password
8) Click Ok.