Try this:
1. First off, make a zip containing all the files inside of the world folder. You can do this by selecting all the files and "archiving" or "zipping" all the files.
2. Upload the world zip to a file upload website. If your world is smaller than 100mb you can use file.io, otherwise we recommend you use Dropbox.
3. Get the direct download link to the file. If you're using Dropbox you can get the share link, but you need to replace ?dl=0 with ?dl=1 at the end of the link. If you're using file.io remember that the download links can only be used once.
4. Run the command /ul world <worldname> <direct link> in your server. Please be sure you don't name your world with any spaces.