I want to cancel my monthly payment for extra mega bill for 2.99 a month please

Apple explains here how you can manage your subscriptions:

How to view, change, and cancel subscriptions on your iPhone, iPad, or iPod touch – Apple Support

https://www.youtube.com/watch?v=mRXvmG8ZpDQ

If you are trying to downgrade your iCloud storage:

• Go to settings
• Click on your name
• Click on iCloud
• Click manage storage
• Click change storageplan
• Click downgrade options in the bottom of your screen

Start here: https://support.apple.com/en-us/HT202039