Wouter,
here are some videos that may assist you in upgrading moodle, specially the last one
http://www.screencast.com/t/7di1TIv9NH
http://www.screencast.com/t/isCbx6rnVd
http://www.screencast.com/t/QfsROwJCz
http://www.screencast.com/t/p59D8pnX8h
http://www.screencast.com/t/BKK0rRLd1
http://www.screencast.com/t/ZtdiUTSrItGX
and if you want to make clones of moodle will also be helpful towards upgrading
http://www.screencast.com/t/aLYYluO8qs