In LPCXpresso IDE - the simplest way to to do this would be to add the linker option:
--defsym=__user_stack_top=__top_RAM2
to MCU Linker - Miscellaneous - Other Options box in Project Properties. You can move the heap in the same way if required, as described in https://community.nxp.com/thread/389026
Alternatively, you can do this by making a minor modification to a Freemarker Linker Script : Freemarker Linker Script Templates
Note that in MCUXpresso IDE, you can do this more directly via a new entry in the Managed Linker script page of the Linker Settings. Please see the MCUXpresso IDE User Guide for more details (downloadable from the Documentation tab of http://www.nxp.com/mcuxpresso/ide
Regards,
LPCXpresso Support