A new version of R (version 3.5.0) has just been released.
Windows users can upgrade R by using the installr package, and running the following R code, as shown below:
install.packages ("installr") # install
setInternet2 (TRUE) # only for R versions older than 3.3.0
updateR () # updating R
A step-by-step tutorial is available here.
Instructions for Mac computer can also be found here.