The workflow to modify elements with Site Designer is different from the typical workflow in Revit.
The following is a general outline of the steps to modify elements in Site Designer. Use this workflow to make the following types of changes to site elements: move, rotate, change elevation, change type, change a boundary (add/delete vertices), and change view scale. Some site elements allow additional types of changes.
To modify a site element
Modify panel, and click the tool for the element to modify.
The following image shows the Modify Street dialog. The Modify dialog for some Site Designer tools is slightly different.

Site Designer updates the site elements as appropriate. Check a 3D view and a section view to understand the results of the changes.