First, if you have an active subscription - you will need to cancel it. Only owners have access to the billing information. Go to your Settings > Billing > Manage Subscription page, and in the bottom corner, click Cancel My Subscription.
Follow the prompts and complete the survey, and make sure to choose Complete Cancellation. You will get a confirmation of the cancellation in your email inbox as well to the owner address on file.
Once you have canceled your subscription, any remaining subscription time in your billing cycle will go onto your account as "trial" time, and you will maintain access to that calendar until that time runs out.
If you are planning on possibly using CoSchedule again in the future on this calendar or if you have a stand-alone calendar - you can stop right here. You are done!
If you would like to completely and permanently delete the calendar and you have connected a WordPress blog, please see this help page for information on deleting your calendar.
For information on completely closing your CoSchedule account go here.