Now, we have all seen what magic can do, the next step is to map your body so you can change it, or revert back to it, yes? this will let you see your body in 'numerical values' and then you can shape change or grow bigger or smaller, of course.
So we have bodies with numerical values of cells, organs and bones and whatever. these are how big they are, and, how much of each chemical they have. now, you need to wish for this to enter your memory so you can change back to yourself as soon as you want to.
Now, we want to map the creature we want to become. you can do this with another wish, of course! be it a bumble bee or a dolphin, you can change into this 'thing' with great difficulty - all you need to do is place your own mass into this thing that you have a good knowledge of - maybe wiki could help you find a study on the animal?
Or, you could say you want to become bigger or something? this would mean taking those values you already have and multiplying them by the values you wish o enlarge by.
Of course, this will require fuel from your cells! this means, of course, that you should be constantly eating as you try to change into a bird of equal mass or what have you.
This also means you need to change your bodies 'makeup.' you could use heat to expand slowly, fuel and heat to expand faster, and fuel, heat and discipline - thinking about the numbers that most affect your new shape or the ones you need to change one at a time.
I suggest a 'combination wish.' this should be for a map of your body, a map of the bodies of the creatures you want to become, and, a gene calculator of sorts; i am sure that a bit of programming research could help you? hell, you all have btter telepathy than me, you can do it!