Replacing installed package with development version in R - r

Question

I'm cobbling together instructions for how to install the development version of a package when I already have the package installed, but I'm a bit confused. My specific need is to install the development version of lme4 so I can use the predict function.
First, I know that I should FIND the development version of lme4, which I've located (in a general sense) at this URL. I'm running Mac OSX 10.6.8 (Snow Leopard), and R version 2.14.1, so I navigate to the correct folder and download the *.tgz file. But when I attempt to install the package using the command:
install.packages("~/Downloads/lme4_0.99999911-2.tgz", repos = NULL)
I receive an error messaging stating:
Warning in install.packages :
package ‘~/Downloads/lme4_0.99999911-2.tgz’ is not available (for R version 2.14.1)
(1) How do I find out which version of R I need to be running in order to access the development version of the package, and (2) How do I update my version of R and/or replace the pre-existing version of lme4?
UPDATE:
I've tried another approach by using the command:
> library("devtools")
> install_github("lme4",user="lme4")
Unfortunately, this yields the output..
Installing github repo(s) lme4/master from lme4
Installing lme4.zip from https://github.com/lme4/lme4/zipball
Installing lme4
Installing dependencies for lme4:
RcppEigen, minqa, RcppEigen
Installing package(s) into ‘/Library/Frameworks/R.framework/Versions/2.14/Resources/library’
(as ‘lib’ is unspecified)
trying URL 'http://lib.stat.cmu.edu/R/CRAN/bin/macosx/leopard/contrib/2.14/minqa_1.2.1.tgz'
Content type 'application/x-gzip' length 945252 bytes (923 Kb)
opened URL
==================================================
downloaded 923 Kb
The downloaded packages are in
/var/folders/IZ/IZlpzJbtHEq7NQxUHPvExk+++TI/-Tmp-//Rtmpt8YCsF/downloaded_packages
* checking for file '/private/var/folders/IZ/IZlpzJbtHEq7NQxUHPvExk+++TI/-Tmp-/Rtmpt8YCsF/lme4-lme4-7a6f816/DESCRIPTION' ... OK
* preparing 'lme4':
* checking DESCRIPTION meta-information ... OK
* cleaning src
* checking for LF line-endings in source and make files
* checking for empty or unneeded directories
* looking to see if a 'data/datalist' file should be added
* building 'lme4_0.99999911-2.tar.gz'
ERROR: dependency 'RcppEigen' is not available for package 'lme4'
* removing '/Library/Frameworks/R.framework/Versions/2.14/Resources/library/lme4'
Error: Command failed (1)
In addition: Warning message:
In getDependencies(pkgs, dependencies, available, lib) :
package ‘RcppEigen’ is not available (for R version 2.14.1)
> install.packages("~/Downloads/RcppEigen_0.3.1.2.1.tgz", repos = NULL)
Thanks! Hopefully my question will be useful to other R novices out there...
UPDATE 2
Based on the output above, I've upgraded to R 3.0.0. However, now I'm getting the following error when I try to install the package I've downloaded:
> install.packages("~/Downloads/lme4_0.99999911-2.tgz", repos = NULL)
Warning in install.packages :
package ‘~/Downloads/lme4_0.99999911-2.tgz’ is not available (for R version 3.0.0)
Installing package into ‘/Library/Frameworks/R.framework/Versions/3.0/Resources/library’
(as ‘lib’ is unspecified)
'.path.package' is deprecated.
Use 'path.package' instead.
See help("Deprecated")