Hi Vince
With an individual or team subscription you have access to a one-time data import from an excel spreadsheet. In order to refresh that data set you'd need the data linking feature which is only available on an enterprise subscription. To learn more about which features are available for each account type please review this Help Center article.
For step by step directions on how to create a diagram based on data and how to refresh the data set please review this Help Center article! Let us know if you have any additional questions.