Verizon's Samsung Galaxy S5 receives update giving it the August 2017 security patch
When you receive the notification telling you that the update has arrived on your phone, before you start the process of downloading and installing it, make sure that your Galaxy S5 is connected to a Wi-Fi signal. If that is not possible, your phone should have a strong hookup to Verizon's cellular pipeline. Also, the battery on the unit should be completely charged before you start the update.
One thing that you won't have to worry about if you own this phone, is getting updated to a new OS build. In May 2016, Verizon updated the handset to Android 6.0.1 Marshmallow, and barring a hack of some sort, that is where it will forever stay.