Q: how do I remove/delete all personal data from iPhone 4S

Setting -> General ->

go to end

Reset -> Erase all content and setting

your iPhone will be like brand new iPhone

If you plan on selling it or giving it away, make sure you turn off activation lock/Find my iPhone.

Covers all eventualities

What to do before selling or giving away your iPhone, iPad, or iPod touch

To remove all settings and information from your iPhone, tap Settings > General > Reset > Erase All Content and Settings. More info here. How to erase your iOS device and then set it up as a new device or restore it from backups - Apple Support

Thanks!!!!!!