R and RStudio are two separate software and each one can have its own version, also, you can't update neither of them without downloading the newer installer in some way. Having said that, the installr package has the updateR() function to automate the R update process on Windows systems.
Or, if you mean updating RStudio without updating R, then you just have to download the new RStudio installer and it should work as long as your R version is at least R 3.3.0 (for the latest RStudio version).