The file manager in the panel is fine for a config file or a few jars. For anything big (a whole world, a modpack, a folder of thousands of files) use SFTP. It's faster, it resumes, and it doesn't time out halfway through.
What you need
- An SFTP client. WinSCP on Windows, or FileZilla on anything.
- The address and port. Open your server in the panel, go to Settings, and copy them from SFTP Details.
- Your username. It's shown in the same box, and looks like
yourname.1a2b3c4d. The part after the dot is your server, so each server has its own. - Your password. It's the one you set at the end of signing up. The panel login is the Discord button, so this is the only password you have here.
Connecting
- In your client, start a new connection and choose SFTP (not FTP).
- Paste in the address and port, then your username and password.
- Connect. You'll land in your server's root folder, the same one the Files tab shows.
Stop the server before you replace a world or a lot of mods. Copying files underneath a running server is how worlds get corrupted.