To upload a world using FTP all you need is the world folder with the world files inside of it.
With the actual world files inside that folder. If you see a playerdata or players folders, usually deleting them is a good idea. With older worlds there might be issues with converting player files.
Also, just so it’s easier in the future, if your world folder has weird characters or spaces it’s better to rename it to a single word. This will just make your life easier down the road.
1. Get your world folder ready.
2. Now connect to your server using a FTP client, and navigate to where your world folder is stored on your computer.
3. Now just upload the world folder you want. (Be sure there is no world folder with the same name already on your server.)
4. Click ok if you get any confirmation windows.
5. Your world should now be uploading to your server.
6. After it’s done, you will see that the world is now on your server among your other files.
7. Now you just need to tell the server to load this world. To do this simply enter the level name of the world for example the world name is flatworld and the level name is main. You would name it main_flatworld
(If you are not adding this as your main world skip these steps and instead use your world management plugin to import this world)