If you know what y = x², you can make the parabola more narrow by scaling this by some constant greater than 1 or smaller than -1. For example, y = 2x² or y = -5x². Note that if you pick a negative constant, you would end up reflecting the parabola across the horizontal axis.
To get a wider graph, you would instead scale by some constant between -1 and 1. For example, y = -1/2 x² (scaling by -1/2, or equivalently scaling by 1/2 and reflecting).
Taking the aformentioned details together, you can (1) reflect and (2) narrow the graph by multiplying y = 3x² by a negative constant larger than 1 in magnitude. For example, y = -15x², where we scale by -5.