In order to manage your FTP users, login to your easyname control panel and navigate to [Web Hosting] → [FTP access].
Here you will see all your FTP users. You can either add, remove or edit your FTP users. Also you can find a link to your [Datasheet] which contains all information needed for a connection to your webspace with an FTP client such as Filezilla.
Please note that you will have to set the password for the respective FTP user in case you forgot it or have never set it before.