I confess, I over-think things. That probably does not come as a surprise

I am trying to start getting fasting by working with my gearing as I ride more. I understand shifting, I've had a manual transmission all of my adult driving life. If you want to go faster, you go into a harder/higher gear. Makes perfect sense to me.

However, the more I try to push it in harder gears, my knees start to complain, and I do not want an over-use injury out of sheer stubbornness. I do that Sign me up for Stubborness Anonymous.

So how do I learn the right way to shift to gain speed without putting my knees at risk by trying to power through it? As a new cyclist my conditioning isn't there yet - but I can't figure out what I am doing incorrectly. Does this make sense?