You appear to be encountering a restriction with a 16-bit machine, which can only access up to 64 kilobytes of memory. To gain more than 65 kByte, upgrade to a 32-bit or 64-bit machine that can handle bigger amounts of memory.
If you're using a contemporary operating system, it will most likely manage memory for you, and you may request RAM as needed using dynamic memory allocation routines. To dynamically allocate memory on the heap in C/C++, use methods like malloc() or new.
If you're dealing with
embedded systems or older hardware that lacks a memory management unit, you may need to manage memory manually and utilize techniques like memory paging or bank switching to access greater amounts of memory.