In Excel (or Word), you can edit a shape after you insert it to your worksheet, either the regular shapes or the customized shapes.
Step 1: Select the shape that you want to edit in the worksheet;
Step 2: Click the "Shape Format" tab in the ribbon;
Step 3: Click the "Edit Shape" button in the ribbon, and then click "Edit Points";
Alternatively, right-click on the shape and click "Edit Points" from the dialog box;
Step 4: Drag the points that outline the shape to change the shape;
Step 5: If you need more points, you can add them to the shape. To add a point, click the shape outline while pressing the key "Ctrl", or right-click and select "Add Point";
Step 6: If you think there are too many points, you can also delete some of them. To delete a point, click the point while pressing the "Ctrl" key, or right-click on the point and select "Delete Point".