To edit an existing dashboard, open the dashboard and click the Manage button in the dashboard toolbar. From the drop down menu, select Manage to enter design mode.
This will open the dashboard design mode, displaying the design grid and the widget toolbox. To change the size or position of a widget, simply drag an drop it in place, or grab the bottom right corner to resize.
The widget toolbox
The widget toolbox is used to add new widgets or edit existing ones.
The ADD tab gives you a list of the available widgets. Use the (add) button to add it to the next available space of the dashboard, or use the (handle) to drag it into place.
The EDIT tab lets you change the widget settings and filter. Click the tab, and make sure the widget you want to change is selected. This will give you two sections.
The widget settings:
which apply to the appearance of the widget.
The widget filter:
where you can set filter properties the applies to the data visible.
If you use custom filtering, it's good practice to activate the display header setting of the widget and assigning it a meaningful name. This way it will be less confusing at a later point that the widget migh not conform to the dashboard filter.
You can at any time exit the design mode to review your dashboard changes. You can do this by closing the widget toolbox, or the button in the top right corner.