Go to the Redmine root directory and run the following command:

svn update

Update the database

rake db:migrate RAILS_ENV=production

rake db:migrate:upgrade_plugin_migrations RAILS_ENV=production

rake db:migrate_plugins RAILS_ENV=production

Clear the cache and the existing sessions:

rake tmp:cache:clear rake tmp:sessions:clear

Restart the application server (e.g. mongrel, thin, passenger)

Thats it.