If a chart is pasted as a picture, double clicking it brings up the format picture window. Work with the chart in the same manner as any other picture.
If a chart is pasted as a linked object, it can be edited directly in Excel by opening the file in Excel or by double clicking the chart in PowerPoint, which opens Excel for you. If a chart is pasted as an embedded object, double clicking it will open Excel so you can edit the chart and the data.
To edit a chart created in MSGraph, double-click the chart and edit the data or change the look of the graph with the formatting features in MSGraph.