If you re-call Samsung changed the way to get into Developer Mode back on the Samsung Galaxy S4, which was not a major change but some people might find this useful!

This will work on the Samsung Galaxy S4/S5 and Note 3.

Go to the settings menu on your GS5.
Scroll down to the "System section and tap "About Device."
Now scroll down to "Build number."
Tap the "Build number" section seven times. (You'll see a warning that you're about to unlock developer options.)
Now back out to the main settings menu, and you'll see "Developer options" listed.

Pretty Simple, from there you can play around with some helpful things you might need for example USB Debugging or Stay Awake and much!