I have an IPhone5s with Straight Talk as my carrier through Walmart. How can I unlock my phone?

Only the carrier it is locked to can unlock it.

How to unlock your iPhone - Apple Support

Talk to Straight Talk and see if they offer unlocking for your iPhone, and what requirements if any they may have.

Only the carrier who owns the lock can unlock it. Anything else anybody offers you is a hack of one sort or another. Apple cannot unlock it as they do not own the lock, the carrier does. There is no law in the USA that compels a carrier to unlock a phone sold locked to their network. If they won't do it, then it cannot be permanently unlocked.

See "how do I unlock my phone" at https://www.straighttalk.com/wps/wcm/connect/StraightTalk/Support/FAQs/Products/ Phone/

Note that iphones do NOT use an unlock code. The procedure is to request an unlock with the carrier, who then instructs Apple to provision the unlock in their activation servers. You then restore your phone as new in iTunes to process the unlock, and then restore your stuff from your backup.

Unlocking a device by any means other than through the carrier it is locked to, while possible, is hack, and not supported by Apple and by extension these forums. We cannot help you with hacking your iPhone to unlock it.

However, do note that these hacks will almost always be undone after every iOS update, or software restore and the iPhone will relock to the carrier it was originally locked to.

Becasue he, just like the person at straightalk you talked to do not know what they are talking about. The carrier is the point of contact you need to deal with to get it unlocked. Apple only processes formal instructions from carriers. They have no legal authority to unlock someone's carrier locked phone without being told to do so by that carrier.

Contact Straight Talk to determine their unlocking policy, and if you qualify.