You can use the Itch App (https://itch.io/app) to download only the changed files, but there's a chance that your manual saves will be deleted (your autosaves will be fine) due to a weird quirk in how the Itch App handles Ren'py updates.
You can use the Itch App (https://itch.io/app) to download only the changed files, but there's a chance that your manual saves will be deleted (your autosaves will be fine) due to a weird quirk in how the Itch App handles Ren'py updates.