I understand how to make a histogram but I have to make a cumulative frequency histogram. I'm not sure about how to change my current intervals. My current iuntervals are 0-2, 3-5, 6-8, 9-11 and 12-14.
The number of whatever you are counting in each iterval would be the height of the bar in the chart that forms the histogram. There will be 5 bars, one for each interval.
You should not change your intervals if your data only has counts in those intervals you mentioned.