Hi Garth,
1 - The URL you sent didn't work;
2 - But I don't think that URL is relavant right now. What you should do is: log in to your Sandbox site (I assume you have the URL to it) and follow the steps they had mentioned:
2.1 - Go to Host Link at the top;
2.2 - Go to Configuration Manager;
2.3 - In the configuration drop down select "web.config" file;
2.4 - The web.config gets loaded. Look for line <htmlEditor defaultProvider="CKHtmlEditorProvider"> it should be on line 288
2.5 - Change it to <htmlEditor defaultProvider="DotNetNuke.RadEditorProvider">
Best regards,
Aderson