I would guess that the image is a static vector image probably produced in some Adobe product (Illustrator?) and then processed through PhotoShop. While you can try to reverse-engineer that and make it a "6" with the same tools, I see at least three options:
First, contact your client's marketing or graphics team and ask them to generate the graphic with the numeral you want.
Second, take the "6th" object in whatever sequence of graphics you are working with, and screen-capture the numeral; then use that same screen-capture program (such as SnagIt) to manually create the graphic as you wish.
Third - and don't rule this out - redesign whatever you are working on so the "5th" item is indeed the normal 5th graphic. Given that your client has provided this graphic in this form, it's likely the most reasonable approach to leave it as it is.
You could also use the screen capture tool to edit out all of the numbers from all of the graphics in that series, and then use SL and manually add them back in the order you are trying to achieve.