hey! you do need to download the whole game after every update, but we make sure to keep them around 100-ish MB each — so this process shouldn't be too much of an inconvenience.
as for your save files, they should be automatically stored in this folder:
C:\Users\Your_Name\AppData\Roaming\RenPy\AnotherChance-1581295674
check if they're there, and if so, feel free to delete the older releases once you download the most recent one!