@BillyJane You will have to contact seedbox provider and if you have SSH access then you can download files from filesharing sites and if at all if they can help you setup rapidleech on same seedbox that will be great and more easy just after you download you will have to move files to your download directory and use for seeding (if i am not wrong that you need them to create torrents).

if you have your own VPS just try once if can build seedbox from quickbox see here it given - https://quickbox.io/

they provide seedbox with rapidleech but for that you should know little about linux and commands to use it flawless.