Follow the steps of your choice:
Use an iOS device
- On your device, tap Settings > General > About.
- Tap the first line, which should display the name of your device.
- Rename your device using the on-screen keyboard and tap Done.
Use your computer
- Connect your device and open iTunes.
- Click the Device button in the upper right corner. (If viewing the iTunes Store, click the Library button in the upper-right corner first.) If you don't see your device, choose Hide Sidebar from the View menu.
- Next to the picture of your device, double-click the name of your device.
- Type the new name for your device and press Return on the keyboard.
- Sync the device (press Sync in the bottom right corner of the screen).