So, here are some advices to help to complete this task :
Upgrade pluginsBe carefull, if you don't upgrade plugins like cache, hibernate, jquery, you will have stranges errors.
Plugin asset-pipeline replace resource pluginYou will have to move directory and organize them in assets directory and also change all include in GSP.Possibles surprises will perhaps appear : see http://stackoverflow.com/questions/27906139/grails-assets-directory-management
Plugin export:1.6To now, it doesn't work for me
TemplatesI delete templates directory end recreate it by command : grails install templates.
It fixes some errors.