Modify Item Description

Dear Experts,

Anyone know how to modify/add some text in the Item Description in Sale Order Form. I'm trying to do that; however, they alway keep asking me to add the new item.

For example

Item A: Orange

Item B: Apple

When I selected : Item A; Orange will show up as the item description

So, I wanna add Orange *Free** or other text

But it did not allow me to do so.

Thanks again.