Editing fill color in an org chart

I have an org chart in which I'd like to change the color of the boxes. I think it was created in Word and saved as a PDF.  

I could export it back to Word but I'd have to ungroup the object and recolor each box.

Here's what I've tried in Adobe:

1. Select shape (box)

2. Right-click, Edit using MS Paint.

3. I select the entire image.

4.  Click on color selection

5.  Click Fill Button

6. Object is deselected and no color change s made.

Any suggestions?

     Sue