Bluetooth name on Android devices is used to identify your device when connecting to other devices and appears on the list of nearby devices, if looked for. To Change Bluetooth Name on Galaxy S5 do as follows:
1. Open Settings application
2. Under Connectivity tab, open Bluetooth.
3. Tap the 3dot icon on the top right and then select Rename Device option
4. Accept the warning which states that you need to change the Device's name entirely, and you can not assign different names for different connectivity methods
5. After tapping Ok, the About Device page is opened
6. Tap the Device Name and change it