Time stretching Accapellas and samples:
Click 'SMP' tab in the channel settings on the right.
'Time Stretching' under 'loop' points light.
Use 'MUL' knob, to left makes it faster, to the right, slower.
Use the 'PITCH' knob to adjust octave of sample.
TIPS: Use sections of samples, cut into bars id suggest.
Hold Ctrl key when turning the knobs, its give you more precise control when adjusting by 1% (Bigups SDM for that tip!).
Turn the 'SNAP' feature from 'LINE' to 'NONE' if the sample doesnt start on beat, just open the piano roll, an manually move the sample to where you want it to start.
Hope that helps