[graph-tool] How to update graph-tool?

Hi, This is really a beginners question :) sorry, but I haven't used version control before... I've got graph-tool-1.1.2 installed on ubuntu 7.10 (compiles with no problems), but would like to upgrade to the latest development source code. I've installed git and typed git clone git://git.forked.de/graph-tool git run without errors and I found a directory ./graph-tool/ with some, but not all, files needed to install. What do I do next? I tried to replace the old graph-tool source files with the new ones and re-compile, but make failed, so I guess this is the wrong thing to do... Many thanks, Rui