Database
[{"product_id":"TEST_PRODUCT","prices":[{"country":"RU","currency":"RUB","value":120},{"country":"US","currency":"USD","value":130},{"country":"UK","currency":"EUR","value":140}]}]
Query
db.collection.update({"product_id":"TEST_PRODUCT"},{"$set":{"prices.$[element]":{"country":"UK","currency":"GBP","value":150}}},{"upsert":true,"arrayFilters":[{"element.country":"UK","element.currency":"GBP"}]},)