Hi Rajesh,
There are two things in refreshing the dashboard,
1. IF you are looking for the dashboard to be get refresh automatically without touching the swf file once its invoked in a day, but the data is getting appended in the DB, then i would suggest you go with xml, webservice or query browser.
Which can refresh you dashboard without touch it.
2. If you need to get the latest data iresspective of other connections then you can use the refresh button component given in dashboards, which helps you to do that.
Kindly revert for any assistance.
--SumanT