You can restore your iPhone to factory defaults. Make sure you backup all you info (contacts, photos…) as it will be wiped clean.
To restore you phone:
1. Connect your device to your computer using the cable that came with it.
2. Select your iPhone when it appears in iTunes.
3. In the Summary panel, click Restore.
4. Click Restore again to confirm that you want to restore your device to factory settings and delete all data and content.