This will remove everything from your device's system, including downloaded apps and files, personal data, personalized settings, and other added stuff. In the process, any software defects and malware will be removed. However, before you begin, make a backup of all of your crucial data. When you're ready, go through the following steps:

1. From the Home screen, select Settings.
2. Select General.
3. Restart by pressing the Reset button.
4. Erase All Content and Settings is the option to choose.
5. To proceed, enter your passcode if required.
6. To confirm the action, tap Erase iPhone.