How to perform SSRS 2005 to SSRS 2008 R2 upgrade
1. Generate full backup for ReportServer Databases in 2005 Instance
2. Backup the SSRS Encryption Key using 2005 Reporting Services Configuration Manager
3. Backup ReportServer .config files from 2005 instance (If there are any customized configurations)
4. Export ReportServer.dbo.Keys table information into a plain text file from 2005 instance.
Now on new 2008 R2 SSRS instance
1. Install SSRS Engine and configure the SSRS using Report Service Configuration Manager
2. Connect to Reporting Services using SSMS to verify everything seems good
3. Stop SSRS Engine and Restore the 2005 ReportServer database on 2008 R2 instance then start it again.
4. Copy the SSRS encryption backup key file to 2008 R2 machine and restore using Reporting Services Configuration Manager
5. If you query the ReportServer.dbo.keys table then you will find machine names of old server name along with new server name, you need to delete the old servers record
6. Restart the Reporting services and verify the ReportManager / Reports URL to view the reports