Hi and thanks for the help!

Accountant was using simply accounting 2008. I've read through the advice here, downloaded Sage 2015. It will only let me open the old files in premium or quantrum. I tried both which seems to work, all our files appear intact while in the 2015 version. After converting the backups to 2015 version, I'm trying to open the backup in Sage 50 pro accounting 2020. I keep getting a message that it has been converted to premium and is not openable by this program.  Any advice on actually getting it to open? What am i doing wrong?