The original installation documentation is here. I strongly recommend reading through it in order to understand where the DETER install process is evolving from:
Since I have generated these images, I have added a few more packages to the meta package for the deter install and bumped the revision. Once you create a bootstrap user and have the repository cloned onto the image, updating should be painless:
cd testbed/install/ports sudo make install cd /usr/ports/misc/instant-deter sudo make deinstall sudo make reinstall