If you need an additional FTP user that only have access to a specific uploads folder.
Example : image designer only allowed to upload to the images folder.
First, log into your Plesk control panel and then click on
Subscriptions from the main menu
Select the domain name.
Now click on the Websites & Domains tab at the top of the page.
Click on FTP access
Select the Create Additional FTP Account
Enter the required FTP details - Home directory can be selected using the folder icon on the right.