How do I use DirectX9 with DirectX10 already pre-installed?

[3 Books 1 Religion]

I want to play a game that requires DeirectX9 but DirectX10 in pre-installed on my ATI Radeon HD 5650 graphics card on my laptop. Is there a way I can switch back on forth as need be between the two DirectX's or do I have to re-install each one every time I want to use it?

I don't know if this helps any but my computer is an Acer Aspire AS5740g-6979. Thanks