You can do it quickly using Global Tuning (in semitones) in either
Preset or Instrument. You can also do it per sample in Instrument with
either Tuning (in semitones) or by changing the root key. For example
changing the root key from 60 to 72 moves it down an octave. The trouble
is that doing it either of these quick ways transposes the samples which
may not be what you want.
To keep the samples right you would need to change both the key ranges
up or down 12 for each sample in Instrument and the root key up or down
12 as well.