I searched the OS web portal for any mention of upgrading from OS 13.2 to OS Leap 42.1. I could not find a single item of documentation regarding this. Is OS Leap a completely different Linux OS from the previous OS 13.2 so that upgrading is not possible, or did I miss something somewhere ?
Yes, it is possible.
If you have moved up to 13.2 from a previous version, then you already know how to do it. It is the same method.
What is “the same method” ?