Hi Anna Martirosyan - Thanks for reaching out over Q&A Forum.
For #1:
Exchanging a reservation enables you to receive a prorated refund based on the unused portion of the reservation. You can then apply the refund to the purchase price of a new Azure Storage reservation.
There's no limit on the number of exchanges you can make. Additionally, there's no fee associated with an exchange. The new reservation that you purchase must be of equal or greater value than the prorated credit from the original reservation.
For #2:
You can also exchange a reservation to purchase another reservation of a similar type in a different region.
I would recommend you start with the below documentation which talks amount exchange scenarios. Thereafter, you might need to raise a support ticket as well for required changes as well.
Hope that helps!
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