Taken from the 0.4.5 devlog above.
How do I keep my saves?:
1 • Go to your current version, start any game, open menu, press “Upload Sync”, save the code and test it in, ( Go to Load, “Download Sync” to make sure it works correctly.)
2 • Install the new Downloader (You can change the name of the app later) .
3 • Let it finish downloading the new version, got to load, go to “Download Sync” and enter the code you generated.
(This is part of Ren'Py. If you get a "Server down" error, just wait for it to fix itself over time)