Only option to downgrade is via the customer care. You can upgrade via website but not downgrade Earlier there used to be an option to downgrade via website and I guess apps also.
I downgraded from Diamond pack to New Gold sports pack last month by calling them. It takes around one week to completely downgrade. First the SD english movie channels were stopped. Then english entertainment the HD channels were stopped.
And you cannot downgrade for 90 days I guess after you downgrade but you can upgrade. (As told by cc on phone while I registered my request to downgrade)