When in a dashboard and wanting to switch to another dashboard, you need to click on Dashboard on the left and then click on another dashboard. I find this not intuitive.
When in a dashboard, the other available dashboards will be shown as a tab on the top row. Clicking on a tab will open the other dashboard.
The available spaces is used with as many tabs as there are dashboard and when there is no more space, two chevrons will indicate there are more tabs/dashboards. Clicking on the chevrons will open a window to the tabs/ dashboards that are available.