You can also use our update data feature. When you are looking at one of your data sets, you will see that there is an option to update the data. You can replace the data set with the newly updated data from your spreadsheet. Once you change the data, all the graphs that have been created will change automatically to display the new data.
Here's an example of a data set that one of our users is updating her data set manually using this feature:
http://www.swivel.com/data_sets/show/1005789