ArcGIS Pro 2.1 "About" Page notified me that an upgrade was available, but every time I tired this upgrade route I got a message "download server error. Please try again later". This would lead you tp believe the server was busy, or connection was too slow, but it turned out this upgrade button works like this unless you have Pro logged into an Organizational account. I thought I was logged into an Organizational account, but it turned out ESRI Sales and my organization had reorganized my accounts. It looks like I am not the only one to have difficulty with this upgrade issue: https://community.esri.com/message/711152-arcgis-pro-upgrade-server-error It's too bad Pro>About will notify you that an upgrade is available, even if you are not logged in to an Organizational account, and then can't deliver. Perhaps the error message could be more helpful. Difficult to find this in the documentation.