How to change from one key to another?

There are 3 basic types of modulations when it comes to adding tonic flavor to your compositions.

1.  This very first one is pretty simple to do and it is called: chromatic modulation.  You achieve this by chromatically increasing or decreasing the 3rd of any of your chords.  An example would be (if in the key of C major), to sharpen the 3rd note of the 2nd chord of the key.  In other words, the 2nd chord would be D minor, and the 3rd note of D minor would be F.  If that F gets sharpened, then you would achieve a modulation to the key of D major or any other key where D major fits.  However, you achieved this by increasing a note by a half step, or chromatically.  You could always come back to the original key by doing the opposite.

2.  The second type of modulation is called: phrase modulation.  This requires little analysis.  Just plan where you want to go and simply go there.  An example could be to simply take your song to any key at any moment for a specific phrase within the song and then come back to the original key.

3.  The third modulation is called: pivot modulation.  This is like the first example above, but instead of concentrating on the 3rd of the chord, you simply concentrate on the whole chord.  That is, keeping the original chord, you make this one chord fit the next key.  In the key of C major, (if on the chord of D minor), simply stay there and make it fit another key.  For example D minor could turn a very nice pivotal transition to the key of F major since D minor is the 6th chord in F major.  You would come back to the original key later by using a pivot chord of F major to return to C major.

The best way to use modulations is to, first and foremost, find the goal you want to achieve with it.  Then, the rest is easy.  Use the techniques above to make some theoretical sense of your modulations and add flavor to your music!!!