Here are the Simple steps to install iOS 8 with iTunes:
Step 1: Connect the i-device to the computer or mac via USB cable and wait for iTunes to launch or manually launch it and recognize your device.
Step 2: Now hit the device button to the left of “iTunes Store” button in the top right corner of iTunes.
Step 3: Click on Check for Update button and iTunes will automatically look for the latest update available for your i-device and install it.
Step 4: At this moment, you will see the pop-up message saying that a new update is available or iOS 7.1.2 will be listed as the latest version installed on your device.
Step 5: If new update is available, then click on “Download and Update” button, or download the correct firmware file for your idevice using
Direct Download links.
Note #1: Disable an “auto unzip” feature in the Safari Browser for downloading the firmware or simply use Firefox or Chrome browser.
Note #2: Find the model number of your device written at the back.
Step 6: Wait until the firmware is fully downloaded. Then hold the Shift key (Windows) or Option Key (Mac) and click on “Check for Update” button.
Step 7: This will launch file manager and prompt user to select the downloaded firmware file. Select the file and Choose Open.
Step 8: You will now see the pop-up message that says that, “iTunes will update your device to iOS 8” and verify with Apple. Just click on the Update button to proceed.
Step 9: Read the release notes information and click Next button. Accept the terms and conditions by selecting the Agree button.
Step 10: Allow the iTunes to download the firmware file which could be time consuming and depends on the internet connection speed. Once the file is downloaded, the contents will be extracted and the device will get prepared for iOS 8 firmware installation.
Step 11: Follow on-screen instructions & wait until the iOS 8 installation completes. Your device may get reboot a couple of times during this process and then you will be able to start using the device with iOS 8
Enjoy!