How to Reset an iPhone Via Computer
Resetting an iPhone involves removing its installed operating system and taking the device back to its original settings. During this process you will lose all songs, videos and applications that are installed on your device. Resetting an iPhone can be necessary to fix errors or free up memory. Resetting an iPhone is a straightforward process that can be done on a computer using Apple's iTunes music software.
Plug the USB cable that came with your iPhone into both your iPhone and your computer. Push one end of the iPhone's USB linking cable into the port on the bottom portion of the iPhone's case. Push the other end of the iPhone's USB linking cable into a USB computer port on your computer. Any available port will do.
Open iTunes by double-clicking on the iTunes icon on your desktop.
Expand the Devices menu by clicking on the small triangle to the left of the word.
Click the name of your iPhone.
Click either "Back Up" if you want to make a copy of all of the personal data on your iPhone on your computer, or "Don't Back Up" if you do not wish to create a backup.
Click the "Restore" button in the dialog box that asks you if you are sure you want to reset your iPhone. Once you do, iTunes will completely reset your device. Once the process is finished, you can put all of your information back onto your iPhone by clicking the "Sync" button.