Make sure that you restart your server after changing world folders (uploading, reseting, etc...)
Website Method
. Go to your server's panel and click the World tab on the website.
2. Under Upload World, click on the button ‘Choose World’.
3. Select the .zip file from your computer and then click on Open
In-game Method
1. Upload the world zip to a file upload website. I recommend you use Dropbox for files bigger than 100mb, otherwise, you can use file.io (Remember that file.io links are only one-time use)
2. 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.
3. Run the command /ul world <worldname> <direct link> in your server.