I t's called transposition and is quite easy to achieve

1. Decide which note you want the piece of music to start on

2.Count in semitones ( up or down ) the difference between the original note and the new note

3. Do the same to all the other notes in the piece of music
eg. 1 semitone up from C is Csharp - 1 semitone up from F sharp is G
2 semitones down from C is Bflat - 2 semitones down from F sharp is E etc.