OTA software update and Samsung Kies are not the only want to update Samsung Galaxy S4. Yes, you can download official Galaxy S4 firmware and install it with Odin software manually. This method works on both I9500 and I9505 model. It is useful when downgrading firmware or upgrade from firmware with custom kernel or custom ROM. By the way, Galaxy S4 firmware is around 1.5 GB file size.
Download official Galaxy S4 firmware