hahaha wow your dreamer. Do not repeat this again as such if not all members are going to label you fluff and just laugh at you. It's phsyically impossible to transform into anything in the physical, material world. It's impossible for magic itself to change your DNA, so sorry no, you can't transform into anything and the spells you have read that say such a thing are fluff and should never have the attention of day.
I believe what Jo here is saying (a little too bluntly if you ask me) is a pretty good summary of the situation. You cannot change yourself physically, by altering your DNA or otherwise. You also can't bring a non-physical being into physical existence.