If you upgraded to the Galaxy S5 from the Galaxy S4 you may be having a bit of trouble getting used to the left capacitive button change. On the S4 it was a menu button, but now on the S5 it is the button for accessing the recent apps menu. If you would rather change the button back to the way it was on the S4 then learn the new button layout, the mod is actually pretty simple. All you have to do is edit a few system files. This does require root so if you are on the Verizon Galaxy S5 this won't be useful for you, however this will work on any other variant as long as your S5 is rooted.
To Replace the Recents button with Menu
-Navigate to system/user/keylayout/Generic.kl
-Edit Key 254 from App_Switch to Menu
-Navigate to system/user/keylayout/gpio-keys.kl
-Edit Key 254 from App_Switch to Menu
To Set Long Press Home to Recents
-Navigate to smali/com/android/internal/policy/PhoneWindowManager.smali
Search for and delete if-ne v2, v5, :cond_6
Via XDA