Hard to know what kind of answer to give here but I hope this helps. If this doesn't answer your question you may wish to have a look at part of my brother's website which belongs to me. It's at http://www.classaxe.com
firstly go to "Friends" and then to "Andrew F." Follow the links to my music theory site.
Simplistically speaking there are two approaches you can make to changing key; a straight key transposition and the modal transposition. These can also be combined. The straight transposition just involves playing the same intervals but changing the root note. e.g
In key transpositions the intervals are always going to be same, in this case WWHWWWH, major.
Modal transposition keeps the root note the same but changes the intervals. Since it is the intervals that make the music I think that the modal approach is much more interesting. If you only want to change one note at a time (this might make your modal approach less jarring) there is a particular sequence of modes you ought to use. This sequence is; Lydian, Major, Mixolydian, Dorian, Aeolian (natural minor), Phrygian and finally Locrian (where the root note itself changes). This can of course be played in reverse order.
There is nothing at all stopping you from freaking out with several notes changing at once. If the root note (i.e. lowest note) is kept the same you can do what you want with the rest of your notes leaving the root as an axis. This is called Pitch Axis theory.
Lydian, Major and Mixolydian all have major chords built from their roots, Dorian, Aeolian and Phrygian all have minor chords built on their roots, Locrian alone has a diminished chord shape built on its root.
The intervals for these are as follows:
Such modes can be found starting from the following notes in the key of C Major:
F Lydian, C Major, G Mixolydian, D Dorian, A Aeolian, E Phrygian, B Locrian.
Other parent scales have different numbers of modes; some of these are duplicates. Take for instance the very simply constructed Diminished Scale which in spite of having 7 notes rather than 6 as in the major scale (counting roots only once) has only two modes. The Intervals are:
WHWHWHWH so naturally shifting up or down these sequence can only produce two modes.
One potentially enlightening way to see how modes differ would be to take a well known tune number each note in order of its pitch (low to high)and then use the resultant numbers to help you transpose it into another mode. Start with a similar mode (e.g. Lydian for Major) and get gradually freakier until the melody is totally bolloxed.