You can stop data collection on any agent machine that you no longer need to include in reports.
From the Report Manager File menu, choose Data, and then select Data Collection.
The Data Collection dialog box opens. All hosts for which data is not currently being collected are listed in the left pane. All hosts for which data is currently being collected are listed in the right pane.
Select the name of the host.
Use the Add, Add All, Remove, and Remove All buttons to move the host names as needed.
You must change the status of collection on the hosts one at a time.
Click OK to save the changes.