I'm currently using CDH 5.5.1 and only notice parcel for 5.5.2 available for upgrading the cluster. I notice that there is 5.6.x and 5.7.x released but they do not show up as being available.
Is there anything that needs to be configured?
Can you let me know your Cloudera Manager version? It could be that the CDH version you inquiring is newer than your Cloudera Manager (CM) can handle; if that's the case you should upgrade your CM to match, or to be greater than your CDH release.