Just below the names of dashboards, you'll see the Filter Dashboard settings. They allow you to apply filters and weighting schemes to all dashlets of a dashboard at once.
To temporarily apply your changes to all the dashlets, use the Apply button (outlined in green below). The changes will revert to their original settings when the page is reloaded.
There are times when you may wish to permanently alter the segment, weighting scheme, or date filters for an entire dashboard. If you only see an Apply button, as shown above, you do not have edit permissions for that dashboard, so you can only make temporary changes to it.
If you have edit permissions on a dashboard, you will see a second button, Save Filters (outlined in green below).
Using the Save Filters button will make the changes permanent for all dashlets.