Both 0.5.X and 0.4.8 save their save file on the same place., so you can delete 0.4.8.
In 0.5.x I've added code that should allow you to open old save files but if you run into problems with this, simply start a new game and use VN Mode (Settings -> Toggle Game Features), Skip 'N Win and Chicken icon to quickly regain you previous accomplishments.