How to clear icloud storage

I hope someone can help me. I have an iPhone and a Macbook. I've been using iCloud for a while. On my Macbook, when I look at the dialog box called Internet Accounts, it shows my iCloud storage is full, 4.99G out of 5G full. I send all my emails using Yahoo Mail. On my iPhone, I have the mail app configured to load the data from my Yahoo account. When I look at the dialog box Internet Accounts, I realized that Mail was checked on both the iCloud account and my Yahoo account. Actually, the only thing I want on the iCloud is Contacts, Notes, Reminders and Calendars. I unchecked Mail from the iCloud and from the Yahoo account tabs. But how do I go in and clear all the Mail data that must already be in iCloud? Do I turn off iCloud on hte iPhone and delete it from Internet Accounts on my Macbook and then start all over? Will that result in my Contacts, Notes, etc getting duplicated? (I don't want that to happen). Any help is greatly appreciated. Please be specific on what I need to do on my Macbook and the iPhone to free up the iCloud storage space.

Thanks!