If you want to continue your singleplayer save with your friends, you can upload your save to your indifferent broccoli Factorio server with these simple steps.
1. Press ⊞ Win + R
on your keyboard.
2. In the run box, paste in: %appdata%\Factorio\saves
3. Press enter and it will open your saves folder. Keep this folder open.
3.5. Stop the server.
4. Open the File Manager
5. Navigate to /saves/
6. Remove all old saves. If you have save data you want to keep, backup the files here.
7. Upload your autosave to this folder.
8. Restart the server and your save will now be loaded.