Q: I no longer have an iPhone, nor do I have pc. I need to downgrade my icloid to free. How do I do this?

Welcome to Apple Support Communities

You need an iPhone, iPad, iPod touch, Mac or PC to downgrade the iCloud storage. The only thing you can do is to contact with iCloud support and tell them to downgrade your iCloud storage > http://www.apple.com/support/icloud/contact

If you can get to an Apple Store they may be willing to sign into your iCloud account on a Mac and downgrade the storage for you.

Of course it's very unsatisfactory that you can't do this from the iCloud website, but under most circumstances it's not a problem.