I am trying to change. I am trying to change background colour of a picture on Adobe Potoshop

Question

I am trying to change background colour of a picture on Adobe Potoshop CS2.I selected a background which then showed a sparkling border around it. Then I tried selecting a colour from Swatch or from the Colour box and doing OK, but the colour of the selection does not change.How do I change colours of selections in Photoshop?Many thanks