Correct order to Upgrade/Update Aurora MySQL Cluster with Cross-region Replica

Hello, We have an RDS Aurora MySQL Cluster with cross-region Replica, and I would like to know the correct order to upgrade them. I have search the documentation but I could not find an statement where it specifies which should be upgraded first, the Replica or the Master. For a minor version upgrade which one should be first ? For a major version upgrade which one should be first ?

Thanks in advance.