How to Wipe Your iPhone of all Personal Data

Clearing all of the data from your iPhone is simple.

1. Go to Settings
2. Tap on General
3. Scroll all the way down and tap Reset
4. Choose Erase All Content and Settings
5. Enter passcode (if you're using one)
6. Select Erase iPhone (twice), confirming that you REALLY want to lose everything

Make sure you have it plugged in, as the process will take quite a long time, "about an hour" according to the warning. But, believe me, it is time well spent!

Once the process is complete, you'll be left with a "factory fresh" installation of the iPhone OS with no trace of you or your data.