How to update unity web player

I have installed Unity web player 4.0.1f2.I want to play “Motorcross Nitro” on miniclip.com.But whenever i try to play it it says on loading screen:
Failed to update unity web player
Errors Details Install Manually
I cleared the cache of chrome and Firefox a lot of times.
My PC specs are:
Pentium4 CPU 3.2 GHz
1 GB memory
Express chippest family VGA 128 mb
Windows XP service pack 2
Directx 9.0

You may have to Install Unity full program as I had the same issue with Formula 1 Online Game and that is what fixed it for me.