1.Identify the report or model you want to change the data source. Note the check box is not used in single update.
2.Choose the SSRS Server shared data source in the column New Server DS
In the example below we are going to change the data source 'master' for the report 'blank' from /ds/DataSource2 to /ds/DataSouce1.
Click on the column New Report Server DS for the data source master. A combo box opens up. Chose the data source /ds/DataSource1. Click the change button on the row.
Below you can see the change. Note in the current Server DS column the data source has changed from /ds/DataSouce2 to /ds/DataSource2