R upgrading on Windows© revisited

From the list:
When I update R the following has worked for me (Windows XP)
1. Install the new version to a new directory (say C:\Program Files\R\R-2.5.1).
2. Rename the new library subdirectory to library2.
3. Copy the entire contents of the old library subdirectory (say
C:\Program Files\R\R-2.4.0\library\ to the new R root to create
C:\Program Files\R\R-2.5.1\library\ .
4. Copy the contents of library2 to library to update your basic library.
5. Now start your new version of R and update packages from the GUI or
from the R console. (You may need to firs check Rprofile .site to
ensure that no packages have been loaded)
6. On occasion I have got warning messages when I tried to load
packages after this procedure. This has been cleared by running
update.packages(checkBuilt = TRUE)
This checks that your packages have been built with the latest
version. When I do this I agree to install all available updates.
7. You may wish to copy various autoloads etc from your old
Rprofile.site to your new Rprofile.site. I understand that there are
some compatibility problems with 2.5.1 and SciViews so be careful.

How to clear screen in R (Windows)

This tip (taken from this old thread) does work only under Windows:

cls <- function() {
       require(rcom)
       wsh <- comCreateObject("Wscript.Shell")
       comInvoke(wsh, "SendKeys", "\014")
       invisible(wsh)
}
cls()

or

# An R function to clear the screen on RGui:
cls <- function() {
if (.Platform$GUI[1] != "Rgui")
return(invisible(FALSE))
if (!require(rcom, quietly = TRUE)) # Not shown any way!
stop("Package rcom is required for 'cls()'")
wsh <- comCreateObject("Wscript.Shell")
if (is.null(wsh)) {
    return(invisible(FALSE))
} else {
comInvoke(wsh, "SendKeys", "\014")
    return(invisible(TRUE))
}
}
cls()

See this StackOverflow Question for other solutions.

What's the best way to upgrade R on Windows©?

Copied and pasted from R for Windows FAQ - Version for R-2.5.0 - FAQ 2.8:

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() in the new R (`Update packages...' from the Packages menu, if you prefer) 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.

Upgrading from R 1.x.y to R 2.x.y is special as all the packages need to be reinstalled. Rather than copy them across, make a note of their names and re-install them from CRAN.