Update for Samsung Galaxy S5 offers improved performance; water resistance failing?
Once you do receive this, we'd stick to the rules despite the comparatively small size of the update. That means you should use a Wi-Fi connection when downloading and installing the update. And we would also suggest that you make sure your batteries are charged to at least 50%.
One thing we do need to touch on concerning this phone, is the IP67 certification. There have been some reports of water leaking into areas of the phone when the device is supposed to be able to be able to withstand a submerging up to 3.2 feet, for up to 30 minutes. Make sure that you have your battery cover securely fashioned and your USB port closed before getting your new pride and joy all wet. Just consider this a friendly warning.
source: MobileSyrup, Phandroid