Reset iPhone 4: Press and hold the On/Off Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears.
Erase your device with recovery mode
If you've never synced with iTunes or set up Find My iPhone in iCloud, you'll need to use recovery mode to restore your device. This will erase the device and its passcode.
Connect your iOS device to your computer and open iTunes.
While your device is connected, force restart it: Press and hold the Sleep/Wake and Home buttons at the same time. Don't let go when you see the Apple logo — keep holding until you see the recovery mode screen.
When you see the option to Restore or Update, choose Restore.
iTunes will download software for your device. If it takes more than 15 minutes, your device will exit recovery mode and you'll need to repeat steps 2 and 3. Wait for the process to finish.
Restarting and Resetting iPhone 4 iphone4
If something isn’t working right, try restarting iPhone, force quitting an application,
or resetting iPhone.
Restart iPhone 4: Press and hold the On/Off Sleep/Wake button until the red slider
appears. Slide your finger across the slider to turn off iPhone. To turn iPhone back on,
press and hold the On/Off Sleep/Wake button until the Apple logo appears.
If you can’t turn off iPhone or if the problem continues, you may need to reset iPhone.
A reset should be done only if turning iPhone off and on doesn’t resolve the problem.
Force quit an application: Press and hold the On/Off Sleep/Wake button on top of iPhone for a few seconds until a red slider appears, then press and hold the Home button until the application quits. On iPhone 3GS or later, you can also remove an application from the recents list to force it to quit.
Resetting iPhone via menu
Go to Settings > General > Reset and select "Erase All Content and Settings"
iPhone 4 IOS 7 menu RESET settings