Although you can update applications on your iPhone directly from the smartphone, you can also download app updates through iTunes on your computer. This is useful if the application update is very large, and downloading from the cellular network is cost-prohibitive or difficult if you have a bad signal. Once the app updates have finished downloading to your computer, they automatically transfer to your iPhone the next time you connect your phone to your computer.
Open iTunes, and then click the "Apps" option underneath the Library section in the side pane.
Click the "# Updates Available" link in the lower-right corner. Click the "Download All Free Updates" button.
Enter your Apple ID and password, and then click "OK" to begin the download process.
Connect the iPhone to your computer by plugging the docking cable into the bottom of the iPhone and the USB connection to your computer's USB port.
Select your iPhone from the Devices list on the left-hand pane. Click "Sync" to synchronize your iPhone to iTunes. The applications automatically transfer to the iPhone if your synchronization settings are configured for application synchronization.
Click the "Eject" button next to the "iPhone" tab to unplug the iPhone from your computer.
To set your sync settings, click the "iPhone" tab in the side window and click "Applications" in the main window. Click the box next to "Sync Applications" and click the either the option next to "All applications" or "Selected applications." To sync selected applications, click the box next to the application's name and click the "Apply" button at the bottom of iTunes.