Update a report's shared data source

gistfile1.cs

string itemPath = "http://servername/sites/reporting/Report Library/My_Report.rdl";
string dataSourceName = "Datasource1";

DataSource[] dsarray = new DataSource[1];
DataSourceReference reference = new DataSourceReference();
reference.Reference = "http://servername/sites/reporting/Data Sources/DATA_SOURCE_NET.rsds";
dsarray[0] = new DataSource();
dsarray[0].Name = dataSourceName;
dsarray[0].Item = reference;

rs.SetItemDataSources(itemPath, dsarray);