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  Function 4AH (decimal 74) is used to increase or decrease the size of a
  block of memory that was allocated by function 48H. Register ES contains
  the segment address of the block that will be changed. Register BX
  contains the desired size of the block in paragraphs (units of 16 bytes).

  The function clears the carry flag if the memory block can be resized as
  requested. If an error occurs, the carry flag is set, and AX contains an
  error code: 07H (memory control blocks destroyed), 08H (insufficient
  memory), or 09H (invalid memory-block address). If DOS reported that there
  was insufficient memory to increase the size of a memory block, BX
  contains the maximum size, in paragraphs, of the memory block.