fix: correct the docs for upgrade_qos

Author: terry-xiaoyu

en_US/configuration/configuration.md

@@ -1753,9 +1753,9 @@ The maximum number of topics that a single client is allowed to subscribe to. `0
 
 #### Description
 
-Allow EMQX Broker to force the QoS level of the message upgrading to the subscribed QoS level when publishing the message.
-
-
+Whether to upgrade the QoS level when delivering messages to subscribers.
+- `off` means "downgrade": delivers using the lower QoS level between the PUBLISH message and the subscription.
+- `on` means "upgrade": delivers using the higher QoS level between the PUBLISH message and the subscription.
 
 ### zone.external.max_inflight
 

zh_CN/configuration/configuration.md

@@ -1715,7 +1715,9 @@ Keepalive 退避指数。EMQX 如果在 `Keepalive * backoff * 2` 的时间内
 
 #### 说明
 
-允许 EMQX 在投递消息时，强制升级消息的 QoS 等级为订阅的 QoS 等级。
+在给订阅者投递消息时，是否升级 QoS 等级。
+- `off` 即“降级”：使用 PUBLISH 消息和订阅中较低的 QoS 等级投递。
+- `on` 即“升级”：使用 PUBLISH 消息和订阅中较高的 QoS 等级投递。
 
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