根据R的官方说法是这样的：

That's a matter of taste. For most people the best thing to do is to uninstall R (see the previous Q), install the new version, copy any installed packages to the library folder in the new installation, run update.packages(checkBuilt=TRUE, ask=FALSE) in the new R and then delete anything left of the old installation. Different versions of R are quite deliberately installed in parallel folders so you can keep old versions around if you wish.

For those with a personal library (folder R\win-library\x.y of your home directory), you will need to update that too when the minor version of R changes (e.g. from 2.6.2 to 2.7.0). A simple way to do so is to copy (say) R\win-library\2.6 to R\win-library\2.7 before running update.packages(checkBuilt=TRUE, ask=FALSE)

翻译过来就是：
先卸载了你的原始版本，装最新版，应该是2.9，安装好了后将原来的library文件夹里面的文件拷贝到新的安装文件中的library下，然后在R中运行：update.packages(checkBuilt=TRUE, ask=FALSE)。
这样就好了。
有私人目录的话还是参考上面的过程，具体的就不说了。


谢谢指导

果然有用，十分感谢

用户目录的这个真的有用，我说为何升级后原来的用户库找不到了……

installr package