What I did:
1. Opened folder with old 0.5 versionI. Loaded save, played a bit and saved.
2. Opened folder with new 0.7 version. Played a bit, saved.
3. Opened
%APPDATA% folder (just type it into your windows search), then Renpy folder
4. Sorted folders by change date.
5. Found two folders that were changed recently (like 5 minutes ago and 2 minutes ago).
6. Backed up files from newest folder (just in case), created 2 min ago.
7. Opened second newest folder that was changed 5 minutes ago, copied all files from it into the newest folder that was created 2 minutes ago.
8. Launched 0.7 and loaded one of old 0.5 saves.