Like many, I have wanted to be taller. I had the same problem that many do which was how can I visualize my desired height when I'm constantly provided feedback that I'm not that height. I decided to try breaking up my desire to be taller into smaller increments. For example, I was 5'9", and I wanted to be 6'4". Instead I focused on just the next inch or half inch. For me, that cut through my inability to believe I was taller. It is a lot easier to believe that you're an inch taller than several inches taller. And then your body is that tall.
This might not have been the fastest way to get taller, but it worked for me. Over the last year and a half I grew to 6'4" like I wanted. I was able to believe I was that much taller and each time more height manifested in my body.
I hope this can help those of you who are seeking to be taller.