It's pretty straight forward Gazza. On the shocks you'll see bellow the spring that there is 4/5 notches, and the shocks will be adjusted with those. You twist the springs to change them into another notch. So if you want softer suspention, you adjust it downwards on the notches.
Or opposite, to make the spring more stiff and thus harder.
Found a picture that explains it straight forward:
I believe the Rebel as a standard comes presett in the 2nd notch (almost at the bottom, so almost the softest notch)
I read somewhere, perhaps in the handbook for the bike even, that you're adviced not to adjust too many notches at once (Ain't 100% sure as to exactly why not, since I can't really see the damage in doing so, but might have something to do with the shocks adjusting to new load setting)
So to jump from 2nd to 5th isn't adviced.
I jumped from 2nd to 4th and tried that a while, and eventually set it to the 5th.
Just remember to adjust both shocks! And at the same number/notch! Might be unplessant if not.
yeah you dont want to adjust too much at once because the spring and stuff need to set/settle. There are technical ways to determine what the right level is - you tube that - it's measuring height just sitting, then with an unloaded suspension and then also when sitting on the seat. there should be some special ratio.
I'm just using the "is my butt more comfy or not" ratio