While it looks a little intimidating, Repetier-Host takes you thru the process of slicing and printing your .stl file 3D creations step-by-step. More importantly, it gives you a nice control panel to operate your 3D printer and send custom g-codes to your printer. It’s free, with versions for both PC and Mac.
This is the program makes it easy when you need to control or update your 3D printer settings and the printer’s built-in control panel is not able to do what you need.