LTE on my new iPhone 5 won't work?

I just bought a used iPhone 5 from a friend. He used to have Verizon but he took the SIM card out. I put my SIM card in and my carrier is Straight Talk. Ever since I got my new phone I don't get LTE but the plan I have gets LTE. I've only been receiving 3G and it's really annoying. Please help me figure out why this is and who I need to contact to fix it or if I can fix it myself.

Have you received lte before? If not then you may be in a non lte area? Check the map for your service. If all else fails for an answer then reset the network or have your company ping the phone if they do that