If you don't remember the email or password for your account, the steps will vary depending on the status of your account.
*When you make a new account, you cannot transfer information from one account to another.
Free Member
If you don't have access to the email address and password on your Niconico account, then we can't help you regain access to that account.
If you need further help,
Contact Support
Premium Members /Paid Channel Subscribers
If you want to cancel your paid services, you can visit PayPal's website and cancel the subscription. Once your PayPal recurring payment is canceled, it stops making automatic payments for online services so that your channel subscription will be canceled as well.