Full video tutorial updating ios 9 .Watch full video tutorial here
https://www.youtube.com/watch?v=qxuwUkoQEu4

Do following steps.
1.Press home key and insert USB cable to iPhone 5 press home key util connect to #iTunes option will show.
2. Tunes software will start automatically if not run you can run it manually .
3 i Tunes will detect iPhone automatically and will show you what you want to update or restore .
4.Click on update and download process will run you can see download link in the right side of the above corner .
4.When download complete do again setups press home key insert USB cable and click on update ios 9.3.4 process will start .
6. process will end in approximately 10 to 15 minutes.
7.Final step mobile will restart automatically and mobile has been updated successfully.