Tariff is set automatically after registration and feed import (it is calculated as a sum of all items in all output feeds, see previous questions).
In case you intentionally decrease the number of items in your feed, you need to let us know at mergado@mergado.com, so that we can invoice you the correct price.
This function is not automated intentionally, because short-term feed outages could result in unnecessary fluctuations.
If the number of items in your feed increases and reaches a higher, more expensive tariff, it is updated automatically at the end of the month.