We’re a bit behind on our release schedule, so the latest official release has become a bit dated. We currently recommend you compile Seal from the master (stable) development branch:
git clone git://git.code.sf.net/p/biodoop-seal/code biodoop-seal-code
Don’t forget to also build the docs (the ones online are for versione 0.3).
If you prefer to use the official release you can download it from here: http://sourceforge.net/projects/biodoop-seal/files/.
And then, see the deployment instructions/suggestions in the section Installation - Deploying.
There is no particular upgrade procedure (but see the notes below). Just build and deploy Seal following the instructions in the section above.