Short Distance Running (Sprint, Other Medium Distance Running) and Long Distance Running (Marathons) are totally different.
You need to get into a good Training Program, which includes Long Slow Distance (LSD) Running to improve your Stamina, as well as Speed Related Work (Running Exercises) to increase your Speed.
Additionally, I would STRONGLY RECOMMEND that you get into a Good Strength Training Program. This WILL INCREASE your STRENGTH and will prevent Injuries…and, WILL IMPROVE PERFORMANCE. I Reiterate Again, that this is in ADDITION to your LSD and Speed Drills.
Please lookup the Internet or work with a Qualified Running Coach to ensure that you are Running using Proper Posture.
Appropriate Running Shoes are a MUST. Replace them IMMEDIATELY, when they are past their Recommended Mileage.
Adequate NUTRITION, that includes Carbohydrates, Good Amount of Protein and Quality Dietary Fat, is Essential.
Rest and Recovery is VERY IMPORTANT TOO. Without this, you will get into Over-training Zone, which is NOT GOOD.