How to reset an unlocked at&t iPhone 5?

So I have an iPhone 5 that was my older siblings. He had it on at&t contract and it's done. I've unlocked it via an outside source (not AT&T) but in USA. But how do I reset the phone(I.e I don't want his apple ID. I want to make my own. Delete all his apps and download my own) basically make the phone brand new "software wise"? I've always used android phones hence i'm clueless when it comes to iphones. I would appreciate the help!
Also IIm not a electronic geek so try and explain it as simply as possible. I d appreciate that.

First, have your sibling remove his iCloud account from the iPhone. Go to this website and show it to your brother: https://support.apple.com/...cale=en_US and tell him to follow the instructions.

After he's done that, go to your iPod and go to Settings>General>Reset>Erase All Content and Settings and follow the prompts.

I'm not sure if erasing the data will have an effect on the unlock status, so keep that in mind.

Settings > General > Reset > Erase All Content & Settings