Here is how to delete all graphics at one time in a worksheet:
Press F5 to display the Go To dialog box.
Click on the Special button. Excel displays the Go To Special dialog box.
Select the Objects radio button.
Click OK. All the graphics in your worksheet are selected.
Press the Del key. All the graphics are deleted.
Thanks to: http://excel.tips.net/Pages/T003018_Deleting_All_Graphics.html