With GameServerKings, becoming an admin on your Factorio server has never been easier. You'll become an admin in no time by following this guide. First, head to your GameServerKings Game Server Management Panel, and click 'File Manager', as seen below:
From there, navigate to the 'Data' folder, and then download the file 'server-settings.example.json' by clicking on the button of the earth next to the file name. When you download it copy the contents by opening it with notepad or any simple text editor. Next, click the 'New File' button at the top, and create a file named 'server-settings.json' within your 'Data' folder.
From there, click OK and it will bring you to a text editor. Paste your contents that you copied from the example page. It should be formatted within our text editor even if it didn't look that way in your notepad. On the final line, there should be a spot for admins, within the brackets insert your Factorio UserName.
Now that you've added that, click 'Save' in the top left corner. Head back to your Manager Panel and restart your server. Once it has booted back up, all UserNames entered within the brackets will be administrators.