When your league is ready to upgrade to a newer version of OOTP, the first step is to open the new version of OOTP, and choose to import the existing league from previous version.
Recommendation: Ideal time in the game year calendar to upgrade is the day after the World Series finishes, before the new Offseason start date. After you convert on that date, advance one day on the new version and OOTP does the new season financial calculations on the new version.
OOTP doesn't support import from anything other than the previous version, so if your league is skipping a version (like OOTP22 to OOTP24), you will need to do an intermediate step to convert to OOTP23.
The location of the import option is right on the start screen of OOTP:
The only update related to StatsPlus for upgrading the version is to update the League Folder setting in the S+ app settings to point to the latest saved_games folder. Setting is here:
You can find your latest league folder by following the steps at League Folder Location.
Once the import is complete, there is one setting to check in OOTP which often is not updated and can cause issues. It's the "Destination folder for archive on local drive". You can find it by going to the Automator, picking League File Center, and looking most of the way down the dialog for the path. Make sure it gets updated to point to your latest saved_games folder.
League File Center option is here:
Destination Folder is here:
After checking the destination folder, upload the league file as usual.
GMs can get to the latest version several different ways: