I have designed a dashboard, then published. But How can I link the dashboard on the top menu ?
1. Create a page (add -> page).
2. Add a portlet to it (add -> portlet -> Dashboard)
3. Click the wrench on top right corner and select "Preferences"
4. Select your dashboard from the list
If you're on old version of UMP that uses the flash dashboard designer, you're going to have to write the name of the dashboard in preferences and it's case sensitive.
Note that with the new dashboards, the usage of the "preload" option only works for the individual who wrote/owns the dashboard. If you are trying to have a page that preloads your dashboard for someone else then they'll always get the "select the dashboard" dialog.
There's an existing defect for this and it's "slated" for 8.2 to be fixed.