Mid-event? Call or text (732) 555-0199 — the line is live from delivery until your return is scanned.
Your kit arrives already loaded and test-printed, so for most events you never touch this. The spare media pack is in the side pocket of the case.
On the DNP:
Release the opening lever, draw the mechanism unit out, and lift out the paper holder.
Fit the new roll so there is no gap between paper and holder, put the holder back, and turn the roll in the direction of the arrow until you hear the buzzer. The flashing orange light going out is how you know it seated.
Close the mechanism unit.
It will now push out FIVE blank sheets on its own. That is the printer initialising the paper, not a fault, and not your media being wasted — let it finish.
On the Canon it is simpler: the paper cassette and the ink cassette both slide out of the front. Keep the cassette under 19 sheets — overfilling it is the most common cause of a jam — and never put a part-printed sheet back in.
If anything does not look like the above, stop and call (732) 555-0199 rather than guessing with a full room waiting.
Two minutes, and you'll know either way.