Hi @chrisv65852847 if you want to downgrade your plan, you'll need to contact Adobe Customer Care:
Go to https://helpx.adobe.com/contact.html and log into the site. Click the chat pod on the bottom right and type AGENT to get a real person who can help. Be patient 1:1 customer care puts you in a queue.
Next, if you have exceeded your 20GB storage currently, I would clean that up before you contact Customer Care otherwise you risk losing files. You have to clean up manually to preserve the collections you want.