PC? If on 0.43.0 - download the 13MB file, extract and throw the 'game' folder into LustHarem 0.43 folder. Make sure the script file in there overwrites the old one.
If not on 0.43.0 already, download the full game, extract and copy and paste the old save folder from the previous version.
If android, simply download and install. Make sure you back up your saves tho.
If Mac, no idea. Don't use that.