Methinks you mean the HP P2055DN printer. Here are the setting involved in adjusting the print density and resolution.
- Resolution: Set it to "ProRes 1200" for highest quality. If it starts to fill in component holes, back it off to "Fast Res 1200".
- RET: Resolution Enhancement Technology. I don't recall exactly what this does, but try toggling it to see what effect it has.
- Print Density: Higher numbers are denser or darker. Lower numbers are less dense and lighter. I think higher is what you want.
- Econo Mode: Save toner but produces "thin" characters. Turn it off.
- Try switching between PCL5c and Postscript. Each has its own "smoothing" algorithm which might affect print density. I suspect PS will be smoother, but incredibly slow to print.
Good luck.