The Cluster Version Operator (CVO) in your cluster checks with the OpenShift Update Service to see the valid updates and update paths based on current component versions and information in the graph. When you request an update, the CVO uses the release image for that update to upgrade your cluster.
https://access.redhat.com/documentation/en-us/openshift_container_platform/4.6/html/updating_clusters/understanding-the-update-service#:~:text=The%20Cluster%20Version%20Operator%20(CVO)%20in%20your%20cluster%20checks%20with,update%20to%20upgrade%20your%20cluster.