How can I train my roller pigeons to fly higher?

[nanglo]

I have about 8 roller pigeons in my coop. I'm not sure what kind they are but I know that they roll. I got 6 of them from my friend and he don't even know what kinds are they and the other 2, is my own breed roller pigeon. They kit together pretty well, but they never seem to fly very high. They only fly as high as a 3 stories building. I let them out usually at 8 in the morning or 7 at night, so the temperature is cool so they won't get dehydrated. Also, I'm guessing that the 6 that I got from my friend are still pretty young because they only either rolls 1 or they just drop or let go of their bodies when they do try to roll. My 2 other home bred rollers, they roll about 3-4 only. Any advice for me so I can get my kit up higher in the sky?