I want to update QuickBooks 2008 files to the latest version. How do I do that?

if you buy from intuit they will do it for free

other wise, make a back up in 08, then it needs to be restored in 2011/12 and another back up made, then that one needs to be restored in 2014/15 and a back up made, then that should restore in 2019.  but if not yet another back up has to be made in 2017/18

Call around as see if anyone has those year versions installed and will help you out

Save a portable file (QBM) on your 2008 software, then use 2019 desktop to restore it.   Worked for me.   No intermediate steps needed.    Did not work with QBW or QBB files.