How do I migrate SQL Reporting Services to another server (2008 to 2012)?

Start SQL Server Management Studio and open a connection to the SQL Server instance that hosts the report server databases. Right-click the report server database, point to Tasks, and click Detach. Repeat this step for the report server temporary database. Copy or move the, this way you can migrate sql server reporting services 2012 Reporting Services Scripter is a .NET Windows Forms application that enables the scripting and transfer of groups of SSRS catalog items from one server to another or from one SSRS folder to another on the same server. Reporting Services Scripter is flexible and lets you transfer catalog item properties, such as serverside report parameters, Subscriptions (both normal and data-driven), Descriptions, History options, and Execution options (including both report-specific schedule and shared schedule execution options) to other SQL Server instances.

Kevin Kline highlights the functionality here and there is a good article by Dale Kelly for migrating reports using RSScripter at MSSQLTips. Another way is to use the power of PowerShell. There are many script available like here and here. There is other utility (which I have not used) called reportsync

SQL server reporting services 2012 SQL Server Reporting Services (SSRS) is a server-based report generating software system from Microsoft. It is part of a suite of Microsoft SQL Server services, including SSAS (SQL Server Analysis Services) and SSIS (SQL Server Integration Services).