I'd agree with B2B Tall, also add 'look at Youtube videos a lot' to B2B's advice, look at Forefoot running, Pose running & Chi running videos, plenty on there & some good tips!
I thought I could change quickly & it doesn't happen fast, when I'm fatigued I still suddenly realise I'm leaning back & heel planting, but, I'm running faster than I was & without the aches in ankle & hip joints afterwards.