Monthly payments or One-off payment

If I pay the 6-month subscription at 130 euros and then after a week I decide to switch to the lifetime subscription of 260 euros, is it possible to pay only the difference of 130 euros, or do I have to pay the full amount?
Or, if I pay monthly subscription with monthly payment of 19 Euros. Can I after 1-2 weeks decide to switch to the lifetime subscription of 260 Euros, is it possible to pay only the difference of 241 Euros, or do I have to pay the whole amount?
When can I stop the subscription? Can I interrupt it after 1 month?
Thanks
Svjetlana