Changing the Default Factorio Map
You may want to change the save/map that your server loads. By doing this, you can have multiple save files and switch between them at your will.
First off, head over to your Gameserverkings Manager Panel. Click the Stop button on your service to turn it off. Doing this while the server is online can cause the current save file to become corrupted or damaged.
Once that's done, click the File Manager button to access your file system.
Now go to the saves folder and use the download (globe) icon to download the default.zip file. Save files in Factorio need to be named "default.zip" in order to be loaded. Once you download the save to your computer, you can rename it to something else temporarily and keep it as a backup.
Once downloaded, you can safely select and delete the file within your File Manager. Then click the Upload button towards the top-left of the File Manager and select and upload the save that you want to use.
With the new save uploaded, click the rename file icon to rename it to default.zip just like before.
Now head out of your File Manager and back to the main manager area. Now you can turn your server back on. It will load the new map!