To complement @mattwarkentin's comment, using .libPaths() is only going to work on your current R session, the next time you start R things are going back to the default locations, so if you want to make this change persistent, you can add this environmental variable to your Renviron.site file, or add the .libPaths() command to your Rprofile.site file.
# Set library path
R_LIBS_SITE="path/goes/here"
Some information about this startup configuration files
https://cran.r-project.org/web/packages/startup/vignettes/startup-intro.html