I have 10 subjects, these are products we sell.

I have 80 days of data (amount sold on that day) for each subject.

40 days of the data are before and 40 days are after a change we made in our store.

The difference between the amount we sell from each product is very big, and there are also many outliers in the daily volumes, my data is not normally distributed at all.

I would like to investigate if there is a significant difference between the amount sold before and after the change.

Should I calculate the average amount for each product for the first 40 and the second 40 days and compare them or just compare the full list of daily volumes before and after?

With which test could I examine if the change had en effect on the amount sold?