Source ServerName: ServerA
New ServerName: ServerB

1. Backup ReportServer and ReportServerTemp dbs from source server ‘ServerA’.
2. Backup RS Encryption key from source server ‘ServerA’. Go to Reporting Service configuration Manager in ServerA. From encryption tab, you can backup the encryption key.
3. Restore ReportServer and ReportServerTemp dbs on New server- ServerB.
4. Configure the Reporting Service thru reporting configuration manager.
5. Restore Encryption key from Source Server to new Server.
6. Perform following process to remove old entries on Key table on new ReportServer db.

Use ReportServer
  Go
  select * from dbo.Keys
  Go
  select * into dbo.keys_old from dbo.Keys
  Go
  delete from dbo.Keys
  where MachineName='serverA'

7. Grant following access to RSExecRole.

USE master
  GO
  GRANT EXECUTE ON master.dbo.xp_sqlagent_notify TO RSExecRole
  GO
  GRANT EXECUTE ON master.dbo.xp_sqlagent_enum_jobs TO RSExecRole
  GO
  GRANT EXECUTE ON master.dbo.xp_sqlagent_is_starting TO RSExecRole
  GO
  USE msdb
  GO
  -- Permissions for SQL Agent SP's
  GRANT EXECUTE ON msdb.dbo.sp_help_category TO RSExecRole
  GO
  GRANT EXECUTE ON msdb.dbo.sp_add_category TO RSExecRole
  GO
  GRANT EXECUTE ON msdb.dbo.sp_add_job TO RSExecRole
  GO
  GRANT EXECUTE ON msdb.dbo.sp_add_jobserver TO RSExecRole
  GO
  GRANT EXECUTE ON msdb.dbo.sp_add_jobstep TO RSExecRole
  GO
  GRANT EXECUTE ON msdb.dbo.sp_add_jobschedule TO RSExecRole
  GO
  GRANT EXECUTE ON msdb.dbo.sp_help_job TO RSExecRole 
  GO
  GRANT EXECUTE ON msdb.dbo.sp_delete_job TO RSExecRole
  GO
  GRANT EXECUTE ON msdb.dbo.sp_help_jobschedule TO RSExecRole
  GO
  GRANT EXECUTE ON msdb.dbo.sp_verify_job_identifiers TO RSExecRole
  GO
  GRANT SELECT ON msdb.dbo.sysjobs TO RSExecRole
  GO
  GRANT SELECT ON msdb.dbo.syscategories TO RSExecRole
  GO

8. Problem- email subscription not showing in reports.
In Reporting Service Configuration, E-mail Settings, provide sender Address, curren SMTP Delivery Method(Use SMTP Server) and SMTP Server Name and apply.
This should resolve the issue.

9. Setting email subscription without using domain like @mycooldba.com

Go to rsreportserver C:\Program Files\Microsoft SQL Server\MSRS10_50.MSSQLSERVER\Reporting Services\ReportServer and edit:
DefaultHostName — mycooldba.com
save it.
Restart SSRS
10. In the all the file share subscription, you have to manually enter username and password for file share credential.
11. Have Fun!

refer site: http://technet.microsoft.com/en-us/library/cc281308(v=sql.105).aspx