Is this for PC or Android?
For PC, it does it automatically. But you can access your saves in the Terrene directory.
For Android you need to copy the save folder from the previous version of Terrene and paste it in the version you want to play.
Eg, Go to your internal storage, Android folder, Data, com.androidterrene_0_0_6, files, and copy the save folder inside somewhere else (Maybe just make a Renpy save folder on your device and store it there.)
Then, you install v0.07 and paste the copied v0.06 save folder into com.androidterrene_0_0_7.
Run v0.07 after, and when you can load your saves in the new version, feel free to uninstall the previous version.
This will only work though, if previous saves are compatible with the latest version of Terrene. I post if they are or not in the change logs