How to Change the Reporting Server Execution Account Password
If the password changes for the account that you specified as the Data Reader Account during the setup of the Reporting server, use the following procedure to change the Execution account password on the Reporting server.
To change the Reporting Server Execution account password
On the computer hosting the Reporting server, on the Windows desktop, click Start, point to Programs, point to Microsoft SQL Server 2008 R2, point to Configuration Tools, and then click Reporting Services Configuration.
In the Reporting Server Installation Instance Selection dialog box, click Connect.
In the Reporting Services Configuration Manager pane, in the left pane, click Execution Account.
In the Execution Account pane, type the new password for the execution account.
Click Apply, and then click Exit to close Reporting Services Configuration Manager.