A vertical change is an upward or downward movement along the y axis. For an upward movement, the number of units would be added while for a downward movement, the number of units would be subtracted.
Given that the original function is
y = 5x - 1,
for an upward change of d units, the function would be
y = 5x - 1 + d
for a downward change of d units, the function would be
y = 5x - 1 - d
Looking at the options, the correct option i