Those instructions work for cPanel hosting, which is what you currently get if you purchase a Linux plan from GoDaddy. If you purchased hosting more than a few years ago, you have classic or web hosting, and there is no way to install a 3rd party SSL certificate.
I have the same issue. Honestly, if I can't have access to adding an SSL certificate myself instead of being forced to purchase one then I'm going to have to transfer my domains and cancel my account. There really needs to be an option to do this and not punish people who have been long time customers. This really is a shame.