In 4/2014 I purchased Lightroom 5 (Student & Teacher Edn). It came with a registration number but not a CD.
I subsequently could not use it (or do any photography for that matter) due to family illness.
I downloaded LR5 without any problem for a 1 month trial to my notebook in 4/2015 to use during an overseas photography trip, after which the trial expired.
I have since registered for Adobe CC (PS, LR) & Bridge on my notebook and the desktop c’ter which is used primarily for photography.
I would now like to install the LR5 software on my other “everyday” desktop c’ter, and pay the upgrade $s as I am now going to retire from academia.
Can anyone tell me how to go about this please?
It is not clear to me what you are trying to do when you mention "pay the upgrade $s" ... the upgrade to what?
You do not need to install an older version in order to obtain/install an upgrade, if that has any bearing on your intentions. You would only need to have the serial number from the older version which you would use as the qualifying version serial number during activation of the upgrade.
In case there is some other reason you want/need to install version 5 then you should be able to get it thru one of the links below...
Lightroom - all versions