I need more flash and SRAM for my LPC 1768 project. Can I add 4M flash and 4M SRAM for LPC 1768? If yes, can I run the code in external flash same as internal flash and use external SRAM in the same way as internal SRAM?
These are questions about the NXP LPC1768 chip - not about Keil tools.
Your first step has to be to study the documentation (Datasheet & User Manual) that NXP provide for their chip...