While making the chart in edit mode, use chart object open, right click
on the chart, chart options, and on the data table tab, check the show
data table box. It will appear on the slide and changes can be made.
If you need to do this during a presentation, my guess is that it will
require VBA code. I am not there yet, others can weigh in here an make
that happen.

With the chart activated, you can show the data table by going to Chart
Options|Data Table (tab) and clicking "show data table."

You can't change the data in the data table, though -- it just doesn't work
that way. The changes will have to be made in the data sheet itself. If the
data sheet has been closed, it can be reopened using View|Datasheet.