How to edit a PowerPoint show (.pps or .ppsx) file. [HowTo]

Your graphics team have send you a presentation that you need to present to a customer. But instead of the usual .ppt or .pptx file that you are familiar with, this one is a PowerPoint show file (the extension is .pps or .ppsx). When you open it, the sideshow begins automatically in full screen. Now, there is something that you have to modify in this presentation and you have no idea how...
Well, it isn't as difficult as it looks and no you don't have to send another email to the graphics team asking for a ppt file.

Two solutions:

1. Change the extension of the file from pps to ppt. Now it will open in PowerPoint. (Not applicable for Office 2007)
   
2. Open PowerPoint. Select Office Button -> Open and browse to your PowerPoint show file. Make the modifications and then save it as a pptx file.