Transpose dialog
Using the transpose dialog, it is easy to transpose the entire score to another key
The dialog uses the circle of fifths to show the possible keys along with the number of sharps or flats corresponding to the key.
Select the desired key using arrow-keys or the mouse. If you were transposing to obtain lower written notes and get messages like 5 semitones up you need to use the octave shift button to change that to 7 semitones down which is probably more of your liking.
By default all keys from 4 flats to 7 sharps are displayed. Use the [7 flats] checkbox to switch to the 7 flats-4 sharps range. Use the Minor checkbox to select minor clefs instead of major keys.
Even text files containing chords may be transposed this way.