How to destroy a big Array and free RAM

Wed Dec 12 08:14:57 UTC 2018

How to delete an array and to free RAM

Hi. Can you help me please?
I have tried many experiments but without success.
I have a big array of arrays (matrix[][]).

After to have filled of data i measure the RAM with an utility 
(for example Wise Memory Optimizer).

Then i try to destroy the array in many modes, but the free RAM 
is still the same.

Can you help me please?
Thank you very much
Giovanni Di Maria