Expand RAM and flash on LPC2294
First you should verify whether you mean SDRAM or SRAM.  I don't think this microcontroller supports SDRAM and I suspect you should plan to use an external SRAM.

Refer to the microcontroller documentation for examples on how to connect the microcontroller to the external SRAM and flash.  You could also find an evaluation board that contains external memories and reference the eval board's schematic.

You will need to configure the microcontroller's External Memory Controller in order for the microcontroller to be able to use the external memories.  Refer to the microcontroller's User Guide for details on how to configure the External Memory Controller.  Basically each memory will be associated with a chip select pin and you will have to configure all the settings associated with the chip selects that you are using.  Typically the External Memory Controller gets configured with some instructions in the startup code for your application.  (It's configured by the startup code so that the external memories are accessible sooner rather than later.)  You will likely have to provide, or at least customize, this portion of the startup code.  Here again, if you can find an eval board with external memories then the example program that comes with the eval board will be a great reference.

Once the External Memory Controller is configured properly, the microcontroller should be able to read and write to the external SRAM without any additional driver code.  The microcontroller should also be able to read from the external flash without any special driver code.  However, writing to the external flash will require some special driver code that you will have to incorporate in your program.  Refer to the flash part's datasheet for the erase and program algorithms that are required to reprogram the flash.  Once again, an eval board example would be a good reference.

(If you don't need to reprogram the external flash at run time then you may not need the flash driver code.  For example, you may be able to get by with reprogramming the flash via JTAG with a special flash programming application on your PC.)

I'm not familiar with the internal bootloader provided with this microcontroller.  I suspect it reads code from the UART and copies it into internal SRAM and then executes it.  I doubt that this bootloader will support your external memories automatically.  But you may be able to get the source code for the internal bootloader and then customize it by adding support for your external memories.