I just read a GeoNet article by Kory Kramer (good stuff, thank you) on upgrading ArcGIS License Server Administrator to 10.5.1 in preparation for the ArcGIS Pro 2.0 upgrade. I still have much to learn about license managers, servers, and alike. Perhaps a basic question, but what is the difference between the ArcGIS License Server Administrator and the ArcGIS Administrator? I upgraded our ArcMap users to 10.5 recently and can see the licensing versions 10.1-10.5 for our products and the expiration date, etc. in the ArcGIS Administrator 'availability' screen. In the ArcGIS LSA 'availability' screen, we are still at versions 10.1-10.4, but with the same expiration date as in the Administrator screen. So this suggests, they are separate but related items, and I should move ahead with upgrading LSA if I want to move to Pro 2.0 without issue? Any input and advice would be greatly appreciated. Thank you in advance.
I would read thru License manager installation and startup—License Manager Guide | ArcGIS Desktop
hopefully that brings you to the LM upgrade. But just in case (and to help others)
Main thing to remember is the license authorization numbers for 10.5+ are different, so you will need to get a new one from you myEsri site. (assuming you licenses were on maintenance at the time of it's release)