help about R

Dear Sir/Madam
Hello

I'm Ph.D student of psychometric at the university of
Tehran.I use R version 1.8.1. I want to upgrade the R
into higher version.I downloaded the latest version
"R-1.9.0.tgz". Unfortunately I could not to upgrade
the R. Could you tell me how I can to upgrade the
R,please?

Best regards
Asghar Minaei

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Yours...Asghar Minaei