Hi Park, maybe your project uses a custom linker scatter file. Please check setting "Options for Target ... -> Linker -> Use Memory Layout from Target Dialog". If this is not set. the new values from the target tab are not used and you need to manually adjust your linker scatter file.
The linker warning "L6312W: Empty Execution region description for region ER_IROM1" does also not tell, you are short of flash space. But it looks like a miss-written scatter file. So, I would start looking there.
Duplicate:
https://community.arm.com/developer/tools-software/tools/f/arm-compilers-forum/48583/mdk-arm-keil-compiler-flash-memory-setting
Thanks for flagging this Andy. Locking this thread.