The latest iOS update is available through over the air update or through the iTunes PC suite. Below are the step to be followed to update your iPhone or iPad to the latest iOS operating system.
Updating iPhone or iPad through the over the air update wirelessly
1. Connect your device to the power source.
2. Connect your iPhone or iPad to the internet via WiFi or through the cellular data network.
3. Goto Settings->General->Software Update. iOS will check for the available updates and download the update files automatically provided your device is connected to power and WiFi network.
4. If there is update available, then tap Download to download the updates.
5. Once you complete the downloading of files tap on to Install to update the iOS.
6. If you chose to download the updates in background, you will get a notification saying the update is available for your device. Tapping to details will take you to Settings->General->Software Update. You can select Install Now or you can leave the installation for later. You will be getting notification badge till update is installed.
Updating the iPhone or iPad through iTunes PC suite desktop application
1. Download and install the latest iPhone PC suite iTunes from here.
2. Connect your iPhone/iPad to the computer through the bundled USB cable.
3. Launch the iTunes application and once it opens select your device in the iTune Device list.
4. Click on Check for update in the summary pane to check for the latest iOS update.
5. If update is available for your device, the iTunes PC suite prompts to download and install.
6. It will take some time to complete the downloading and installing based on your data speed. Do not disconnect your device till it complete the process.
7. Now your device is updates to the latest iOS update iOS 7.