Not old, but nowhere else will say...

Having got nowhere with my Suffolk Super Colt, I had to mow the lawns with something so out came the electric, a Qualcast Concorde 32, the slightly older, squarer model with wheels up front, not a roller.  I need to adjust the bottom blade as the main blades aren't even touching it, but I cannot find any advice on the 'net anywhere.  Can someone help?  I see there's a nut on a threaded rod either side of the cutter drum, but is that to move the cutters down or the bottom blade up?

With the Colt refusing to re-start the very day after it cut the back lawn, I had to use something on the front lawn to keep up with the neighbours and despite going round twice with the electric it still looks like a bit of stripey shaggy teddy bear fur, but at least I made the effort!.  Neighbours!  Never had any before!

Thanks for the help.

Martin