How do I reset a brother HL 5450 printer - Brother HL-5450DN Laser Printer

Here is how:

1. Turn off the machine.
2. Make sure that the front cover is closed and the power cord is plugged in.
3. Hold down Go as you turn on the power switch. Keep Go pressed down until all the LEDs light up, and then the Ready LED turns off.
4. Release Go. Make sure that all the LEDs turn off.
5. Press Go six times. Make sure that all the LEDs light up to indicate the print server has been reset to its factory default settings. The machine will restart.

Try download manual from brother site:
http://support.brother.com/g/b/manualtop.aspx?c=eu_ot&lang=en&prod=hl5450dn_all

it is something specific what you want reset? toner? drum? or the printer? all of that is available in manual.