By default Guvnor assumes to find Designer under localhost:8080, see docs: http://docs.jboss.org/jbpm/v5.2/userguide/ch10.html#d0e3136 to see how to configure both Designer and Guvnor to change the default settings (as you mention you have done the Designer part already).
With Designer 2.1 close to releasing I would also recommend to replace your 2.0 wars with 2.1 candidate release available at people.redhat.com/tsurdilo/designer/master and test with that as we have fixed numerous issues around execution of the BPMN2 produced by Designer since 2.0.
Don't forget to clear your browser cache after replacing your current war.
Hope this helps.
I've read your reply and looked trough the link you posted.
I've opened drools-guvnor.war but I can't find any file named "preferences.properties" in WEB-INF
I've created a new one and copied the code from 10.5.2 chapter of the manual (modified localhost). Then I zipped the directories (.war) and deploied the package, but this doesn't work (also with designer 2.1 )
In the end of the chapter 10.5.2 I've read "you have to deploy Guvnor as exploded archive".
How can I do this?