option 1) swear at it
option 2) as above get a second person to push down on the front of the bonnet when you pull the level
option 3) with the drivers door open, pull the lever all the way, hold the lever out, thump the bonnet with a fist about halfway along near the guard (people look at you funny but it works 95% of the time)
Depending on what's not adjusted correctly depends on the fix:
It could be the main part in the centre of the bonnet that latches need to be wound out, undo the lock nut and use a flat head screw drivers to wind it out then do the lock nut back up.
It could be someone has wound the rubber stops out to far so that the bonnet looks like it sits flush with the guards and hold to much pressure on the latch, i wouldn't recommend playing with these unless you have patience and can adjust them slowly without slamming the bonnet closed and push down on each side to check the clearance between the bonnet and headlight (i wound them in to far once on a vp and when the bonnet was let go to close it shattered a headlight....)
It could just be the cable is old and stretched, get a new one before it breaks and you can no longer open the bonnet at all.........