How to install git 1.8 or above on Debian Wheezy
I would definitely recommend using the backports version. To use the backports repository, keep in mind that you must add the following line to your /etc/apt/sources.list:
deb http://http.debian.net/debian wheezy-backports mainAnd then you can retry with apt-get. You will find full instructions at http://backports.debian.org/Instructions/#index2h2
Clone it from its repo https://github.com/git/git and compile it yourself. I've done it on Cygwin and it was easy, so it should be OK on Debian. Read the INSTALL file, it is fairly self-explanatory.
If you haven't compiled software before you should know that there will be quite a few pre-requisites required (they are listed in the INSTALL). You should just be able to apt-get them.