here's a cool little trick to change keys up a minor 3rd. begin on the I and make sure to end the phrase on the IV. then, pivot up a minor third up from the tonic and write like you're in Eb major (this is called modulation). notice that the IV in C becomes minor to fit the new key and hence becomes the ii in Eb. quickly resolve to the tonic with a V - I (or any other variation) cadence to establish the new key. congratulations, you've changed keys up a minor third!
