Can the Major Version of a DCS Redis Instance Be Upgraded, for Example, from Redis 4.0 to 5.0?

Yes, but only from a DCS Redis 3.0 instance. For details, see Upgrading Major Version of a DCS Redis 3.0 Instance.

No. It is unavailable for DCS Redis 4.0 and later. Different Redis versions use different underlying architectures. The Redis version used by a DCS instance cannot be changed once the instance is created. For example, you cannot change a DCS Redis 4.0 instance to Redis 5.0. If your service requires the features of higher Redis versions, create a DCS Redis instance of a higher version and then migrate data from the original instance to the new one. For details on how to migrate data, see Migrating Data with DCS.