First, work out the BPM of the sample u want to time stretch. Then go to PROCESS> down to TIMESTRETCH then click.
In the INPUT FORMAT drop menu, select BPM. Underneath is INITIAL BPM. In that window put in the original BPM of the sample.....Than above that is the final tempo window. This is where u put the new BPM at which u want the sample to fit. Try and stay within 8-10% of the original BPM to avoid loss in sound quality and realism. Above the window is a drop menu window called MODE. In here there a various presets you can use to satisfy the effect of your timestretch. I tend to use MUSIC 2 or 6.
My advice would be to preview the effect before confirming tho.
Thats about it
I'm using 5.0 and there is a drop down for input which let's you choose between time, BPM, %, etc. Once you set that to BPM just follow Bravo's instructions above.