Hello,
The functionality to backup/restore the log retention time was introduced only in Adaxes 2013.1. The log retention time wasn't restored when you upgraded because previous versions of Adaxes didn't store this information in the backup file. Starting from Adaxes 2013.1, the log retention time is stored in Adaxes service backup file and restored together with Adaxes service configuration.
As for the log file itself, it is included into the backup file generated by Adaxes. So, if you have a backup file from which you restored Adaxes configuration, you can change the log retention time of your Adaxes service to whatever number of days you need, and then restore your Adaxes configuration from the backup file. This will also restore Adaxes service log.