Sometimes the key of a song is not ideal: it is either too high or too low for the singer or difficult to play for the musicians. In that case you have to transfer the key of the song to a new key that is a better fit: this is called transposing a song.
How do you do that?
You first take the original key and then try to find a more suitable key step by step: up if the music is too low and down if the music is too high. Using the chromatic circle below you then find the new suitable key. Each step in the circle is equal to a semi-tone in music. If you would like to transpose upwards, you move clockwise in the circle. If you want to transpose downward, you move counter-clockwise.
Example: you would like to transpose your song from the key of E (downwards) to Db. From E in the circle, you take 3 steps counter-clockwise to Db (in the circle this is 3 steps up on the right-hand side!)
When transposing sheet music to the new key, you have to transpose all chords and notes to the new key with the same amount of steps as above. In some cases musicians only work with chords, in that case you only need to transpose the chords.
If reading music or transposing is not quite your forte, I have a handy tool for you to help you transpose. With this tool, you can easily compare the old notes with the new one and use it for transposing. I have not included all keys in the tool, only the most-used ones as musicians are usually not very eager to play music in keys with many sharps or bs.
Noten transponeertool Nederlands
Transposing tool English
After finding the right key for you, you make a transposition set-up lining up the notes of the original key opposite the notes of the new key. You then replace all the old chords and notes with the new ones using the set-up.
Remember to add the appropriate amount of sharps (hashtags) or bs next to the clef at the beginning of the piece to mark the correct key signature. You are all set to go!
EN 
NL