[{"_id":ObjectId("5a934e000102030405000000"),"guild_id":1234,"members":[{"member_id":"001","name":"John Doe"},{"member_id":"002","name":"Bob"},{"member_id":"003","name":"Sam"}]}]

db.collection.update({"members.member_id":"001"},{"$set":{"members.$.name":"John"}},{"multi":false,"upsert":false})