how to reset an iphone 5

You'll need your password to do a reset.

See If you forgot your Apple ID password https://support.apple.com/en-us/HT201487

You also can use Having trouble signing in/iForgot https://iforgot.apple.com/password/verify/appleid 

And you will need to see If you forgot the answers to your Apple ID security questions https://support.apple.com/en-us/HT201485

Before trying to answer your security questions is very important that you think about your questions, including your birth date, and their answers carefully and try to recall all details you can. If you don't answer them correctly enough, then you easily can lose control of your account.

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If you can recover your password, then use How to Erase (and restore) your device to factory settings)

 iPhone, iPad, or iPod Touch https://support.apple.com/en-us/HT201274

If you forgot the passcode.

Passcode - If you forgot the passcode for your iPhone or your device is disabled.