If you would like to use a different image on the buttons on the New Order page you can upload your own images and assign them to particular products.
Instructions
Go to the Settings > Products page.
Click on the 'Add Custom Product Icons" Tab.
Click the Upload Icons button.
On the page that loads, you enter the name of the icon (for your own reference) and then select the image file.
You can then adjust how the icon will appear, alongside being able to see a preview of how the icon will look in the upper right-hand corner. Once complete, click 'Add Icon' to upload.
After you have uploaded your icon you will be able to assign them to products on the Settings > Products page.
*Please note that you will not be able to delete a custom icon once it's uploaded. You will however be able to change the icon of a product.*