If you just want to create an application that you download and run in RAM, then you can either remove the flash section from the memory map in the Memory Configuration Editor (documented in the LPCXpresso IDE User Guide), or else tick the "Link application to RAM" option in
Project - Properties - C/C++ Build - Settings - MCU Linker - Managed Linker Script
But if you want to create an application built for flash but where some of the code is relocated and executed from RAM, then the FAQ gives some details of how to approach this: https://community.nxp.com/message/630746
Regards,
LPCXpresso Support