How do you calculate change in net working capital?

How do you calculate change in net working capital? Specifically I am working on case study for Procter and Gamble investing in crest whitestrips advanced seal and I have to know how to calculate change in net working capital but don't know how. If you look up that case in course hero, I am using one of your examples for the presentation on it and I am on the excel slide with base case valuation. please help!