Uninstalling Operations Manager Reporting is relatively simple, you do it through Add/Remove Programs in the Control Panel. There is a little more to it though...
Firstly: Take note of the Application Pool settings for the ReportServer and Reports visrtual directory in IIS Manager and all configuration settings within SQL Reporting Services configuration. Screen shots are best used for this task.
Once Reporting has been removed, you must delete these databases: (Use Transact-SQL or SQL Server Management Studio)
OperationsManagerDW
ReportServer
ReportServerTempDB
When deleting the databases make sure to check the option to close any existing connections or it may error on you. Once complete now to delete the Application Pool and virtual directories in IIS.
Open IIS Manager. Expand the Default Website. Access the properties for the ReportServer virtual directory. Map this from the ReportServer Application Pool to DefaultAppPool. Repeat for the Reports virtual Directory. Now expand Application Pools and delete the ReportServer Application Pool.
Lastly, delete the ReportServer and Reports virtual directories.
Next Access the Support Tools folder from the OpsMgr install media and copy resetsrs.exe to the hard disk. Open a command prompt and launch resetsrs.exe.
The Syntax is: resetsrs SQLinstance <Enter>
If you left default when installing, the command will be: resetsrs MSSQLSERVER <Enter>
Enter the account name with Admin access to SRS when prompted and the password.
This should actually re-create the ReportServer, ReportSeverTempDB databases as well as the ReportServer Application Pool, and the ReportServer and Reports virtual directories.
Confirm that both virtual directories are configured to use the ReportServer Application Pool.
Now run SQL Reporting Services configuration. Make sure that all elements are configured as they were previously. You will likely at a minimum need to re-configure the Web Service Identity.
To test make sure that you can access the http://SRSSErvername/reports and http://SRSServername/reportserver web pages, if yes, you're in business re-install Operations Manager Reporting and Bob's your uncle!