...

1. Open RStudio
   
   
2. Navigate to Tools > Global Options...
   
   
3. On the Options menu, click on Packages located on the left-hand menu
   
   
   
4. Under Primary CRAN repository, click Change
   
   
   
5. Under CRAN Mirrors, click on Global (CDN) - RStudio
   
   
6. Click OK
   
   
7. Click Apply

Installing Older Versions of Packages

Using Devtools to Install Older Package Versions

1. Open RStudio
2. Click on File > New File > R Script
3. In the script window, type require(devtools). Then on the next line type,  install_version(package name, version = #, repos = "http://cran.us.r-project.org")
   1. Example: install_version("ggplot", version = "0.9.1", repos = "http://cran.us.r-project.org")

Installing an Older Package From Source

1. Open RStudio
2. Click on File > New File > R Script
3. In the script window, type packageurl ← package url. Then on the next line type,  install.packages(packageurl, repos = NULL , type = "source")
   1. Example: 
      1. packageurl ←  "http://cran.r-project.org/src/contrib/Archive/ggplot2/ggplot2_0.9.1.tar.gz"
      2. install.packages(packageurl, repos=NULL, type="source")