How to Discontinue 'Monthly Paid Plan' in Second Month

How to Discontinue 'Monthly Paid Plan' in Second Month

Hello, 

I want to upgrade to 5000 subscribers ($45) plan & use for the first month only. Means, I don't want to continue this plan (5000 subscribers) for the second month.

Can you provide an information of how I would discontinue this plan as early as possible in the second month so I won't be charged $45 amount automatically?

I would be waiting for your prompt response.

Thanks in advance.