Well, the thing is that potential ability is tied to VO2max. I would hope that we all know that. And VO2max is reached when you are at your breathing limit and cannot get any more oxygen into your body. So if you're not there with your lungs, you need to improve your muscles' ability to use oxygen, i.e. get stronger and more efficient, i.e. more mitochondria, more capilarization, more muscle mass, more neuromuscular conditioning, all that stuff, which translates as hill intervals, flat intervals, gym work, and in general, learning how to train. It's a big subject.
Or forget the whole thing and just have fun riding your bike.