How much of a RAM we can use in our program

I'm using LPC1768 controller keil v5.24.2.0. In the LPC1768 controller i put tcpip,http stack and some other application to it. While executing data memory reaches around 32700 it works well. But after that it gives an error".\Objects\IIOT Raw.axf: Error: L6406E: No space in execution regions with .ANY selector matching server.o(.data).". Before reach the error the memory limits are Program Size: Code=35844 RO-data=31472 RW-data=300 ZI-data=32348.
But in a datasheet they given the data memory is 64K. How to use the full of that ram memory?</br></br>

Thanks & Regards,

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