Need help re-installing Sage 50

Had to get some work done on my computer and although they did a backup it looks like a older version of sage is all that remains.  When I try to load my company files |I get a message the file was created by a previous version of sage and I will need to update.  When I click on the sage icon I'm told that it's a trial version.

Is there a guide for re-installation somewhere?

NB