如何在Linux Mint 17.1上安装R 3.1.2

I have installed the latest version of Linux Mint (17.1) in my computer. I installed R version 3.0.2. However, when I try to install the package xslsx, or dplyr, the system says that these packages are unavailable for the R version I have, and that the shall be installed on the R 3.1.2 version. 've been trying to upgrade R from all the possible means but I haven't had a sucessful result. Is anyone experiencing the same problem?I have installed the latest version of Linux Mi