How to Change IIS ReportServer Application Pool Account Password
If you change the password for the account that you specified as the Data Reader account during the setup of the System Center 2012 – Operations Manager Reporting server, you must change the IIS Report Server Application Pool account password. You can accomplish this by using the following procedure on the computer that is running SQL Server Reporting Services.
To change the IIS ReportServer Application Pool account
On the computer running SQL Server Reporting Services, on the Windows desktop, click Start, point to Programs, point to Administrative Tools, and then click Internet Information Services (IIS) Manager.
In Internet Information Services (IIS) Manager, expand <Computer Name> (local computer), expand Application Pools, right-click ReportServer<INSTANCE>, and then click Properties.
In the ReportServer<INSTANCE> Properties dialog box, click Identity.
In the Password box, type the new password, and then click OK.
Close Internet Information Services (IIS) Manager.