How to add new Dimension Attributes to the existing dimension through BIDS

Assuming that your DSV includes the columns that you want to add as attributes, and assuming that you have an existing dimension, you cannot open the Dimension Wizard again to add more attributes to your dimension. Instead, on the Dimension Structure page (as shown in Diego's screen shot), you have the Attributes pane on the far left where each attribute is listed and you have the Data Source View showing the diagram of your table. You drag a column from the diagram on the right to the Attributes pane on the left. That creates a new attribute.

The image above shows the cursor appearance as you drag the column into the Attributes pane. The image below shows the Attribute pane after you release the mouse button - the new attribute appears as shown.