In AX 2012, the old SSRS reports for AX 2009 is stored in the AOT node "Report Libraries". We can find it all in the view 'Application Explorer' of visual studio, but we can't modify it as usual. Refer to the MSDN's essay, if we want to modify the old SSRS reports from AX 2009 in AX 2012, we should upgrade it from ''Report Libraries" to "SSRS Reports" by using command line tool.
The command line tool is installed in the AX client root path. The default location is "C:Program Files (x86)Microsoft Dynamics AX60 ools".
The syntax for the command tool is "UpgradeReports [command] –t [target directory] <options>".
Example: Upgrade the AX 2009 SSRS Report from project files.
More information refer to https://technet.microsoft.com/en-us/library/hh292607.aspx.