Question

suppose the axis of the earth was not tilted .what difference

Answer 1

There would still be seasons, as in a yearly variation in weather - but they would be different.

For one, day length would not change - everywhere would always experience 12 hours of day and 12 hours of night (well, plus or minus a few minutes depending on where Earth is in its orbit, because of the effect of the angle to the sun moving due to the motion in the orbit).

Also, the seasons would be the same everywhere, and they would be at different times, especially for the northern hemisphere.

Answer 2

if the earth was not tilted the seasons would be still, as in early variation in whether.
for one day length will not change.