I need to adjust the deck on this mower. Does anyone know where I can get the manual or instructions please?

Found the two adjusting wing nuts at the rear bottom of the deck. I first lowered the blade on a flat surface, the tightened these wing nuts. I still have a little adjusting to do, but this is where you adjust the deck on the Murray 42inch (1999) mower.

Hi,
You did not give a model number(never helpful) so I had to select a representative manual to reference for you. Check page 28 at the link below:
Murray Lawn Tractor Instruction Book | ManualsOnline.com
Peace,
Clarke