Hello,
all you have to see is the coefficient of x²:
if positive: upward
if negative : downward
y=-3x²+4x ==> -3: downward
y=1-2x+6x² ==>6 : upward
y+x²=-x-2==>y=-x²-x-2 ==> -1: downward
y+2=x² ==>1: upward
y-2x²=-3==>y=2x²-3 ==> 2: upward
y+2+3x²=1==>y=-3x²-1 ==> -3: downward