Struggling on the same thing, FTP part is easy to use just download Filezilla and use the FTP config on the Dashboard of Nitrado. I have tried plenty of things to try and get it working but it keeps coming back with "Error starting dedicated server: GameWorld "North Romexamu Territory" not found!"
I have placed the world name as the Game World name as well as the save now, I have created World and Generated World folders and tried putting the world in there, I have also modified the serverconfig.xml to have property name="UserDataFolder" and set it to the folders i created but so far at a complete loss.
The below companies have their own guides but Nitrado do not and these other guides I have tried to implement on Nitrado.
Ping Perfect - 7 Days to Die | Uploading an Existing world - Knowledgebase - Pingperfect Ltd
Nodecraft - How to upload a singleplayer world to your 7 Days to Die Server | 7 Days to Die | Knowledgebase Article - Nodecraft