Is there anyway i can use micro-controllers flash memory as a RAM as i need 150kB of buffer but controller has 32kB of RAM and 512kB of Flash? Also can i use this ram as stack or heap?
No, flash is flash, RAM is RAM.
The micro can probably program its own flash if you needed to calculate a look up table or similar, but you can't use it as you would a RAM.
The RAM you do have can probably be configured as stack and heap, these sections will be defined in a linker script, the format for which is toolchain dependant so check your compiler and linker's manual.