launching R in AWS EC2

I am trying to launch an R instance in AWS EC2. I have opted for the free tier and use the Amazon Linux AMI. In user data I have specified in the following manner to install R and Rstudio:

    #!/bin/bash
    # install R
    yum install -y R
    # install RStudio-Server
    wget https://download2.rstudio.org/server/centos6/x86_64/rstudio-server-rhel-1.2.5033- 
    x86_64.rpm
    yum install -y --nogpgcheck rstudio-server-rhel-1.2.5033-x86_64.rpm
    yum install -y curl-devel
    yum install -y openssl openssl-devel
    # add user
    useradd forecasting
    echo forecasting:testing | chpasswd

However, the R version is not the latest one - how do I modify this code to download the latest version of R?