Stop your game server before uploading your world.

Follow the Guide (How to Edit Files Using FileZilla FTP) to connect via FTP by using your Game Server login details.
You can find your login details on the Game Server page (see the "FTP Username" section).



After connection is successfully established, you will see two sections. Files stored on your PC are displayed on the left, and those stored on the server are displayed on the right. By using the left section, navigate to a folder where your world folder is saved. By using the right section, navigate to the server folder. Next, copy the world folder from the left section (your PC) to the right section (Server).