Is it possible to change my DNA?

Is it possible to change my DNA? How dangerous is it? Can enviromental factors contribute to it?

First of all, DNA changes on its own all the time.
There are some enviromental factors, like viruses, that can change your DNA.
DNA can be changed intentionally. Look at dogs and selective breeding. It is possible for humans to manipulate the actual genetic code of an organism, but we most likely won’t get taller or smarter by doing so.
I would say this would be quite dangerous, considering that we do not have a deep enough understanding and control over genes.