if(!require(installr)) {
install.packages("installr"); require(installr)} #load / install+load installr
# using the package:
updateR() # this will start the updating process of your R installation. It will check for newer versions, and if one is available, will guide you through the decisions you'd need to make.
Links:
http://www.r-statistics.com/2013/03/updating-r-from-r-on-windows-using-the-installr-package/
