Currently InstaCharts is geared toward spreadsheets that require little editing. Some editing capability does exist as explained below.
To edit data in individual Sheet cells, click the Data tab. Next click the Edit button in the upper left side of the Sheet toolbar. The Sheet is now in Edit mode. Double click in a cell to edit its data. Once you are done making edits, click the Save button in the Sheet toolbar. The edits will be saved and applied to all charts in the Sheet.
Column names are editable via the Edit Columns panel in the left sidebar. Make sure to click Save after you are done editing names!
Functionality to add new rows and delete them are coming soon!