To decrease an item in a list, you can simply subtract a certain value from the original value of the item in the list. For example, if you have a list called "numbers" with the items [5, 10, 15, 20] and you want to decrease the second item in the list by 3, you would subtract 3 from the original value of 10 to get 7. The updated list would then be [5, 7, 15, 20].
