>how can I control the DRAM with PIC?
>how can I do  refresh the DRAM?

There used to be various DRAM controller chips which did the address
multiplexing and refresh control all in one package. Intel used to make one, but
that was a long time ago. Texas Instruments also made one, again a long time
ago.

I suspect that if you really need this large amount of ram, then the PIC is not
going to be the processing element you need. It is going to take a reasonable
amount of your code space to just manage that size of ram.