You can control the frequency of your subscription and the next charge date directly from your account settings. Head over to the 'Subscription' section under my account, you will find all your active subscriptions listed under this section.
Frequency change is calculated from the date of the previous charge
In case you'd like to update the frequency before your upcoming charge, you must do it 48 hours prior to the upcoming charge
Example: If you were last charged for your subscription on 10th May and the original frequency was 1 month, your next charge would have been due on 9th June. In order to change the frequency to 2 months, you must change it by 7th June. Once you change the frequency to 2 months, your next charge will be due on 9th July (i.e 10th May + 2 months)