Adjusting rear shock on Pulse Adrenaline 250CC - is this a modification?

Hi Guys,

I'm looking at taking a pillion on my 250 but I think the rear shock will be too soft, I have had a look and can see no way of adjusting (on my Yamaha it was just a preload nut with five settings)

Any advice please guys on how I can make the adjustment to make the suspension a bit harder and what is required?

thanks in advance
WasNotWas