How to I make my program release memory?

[wavic]

As you say using flash memory for swap isn't good cause multiple write operations. You didn't tell that that is the case. 
Anyway, you can check memory usage for application with top or htop command. The second one is more convenient but might be not installed. If 1GB suites you you may repeat the creation of the file, format it as a swap space and activate it again. If you keep path and the file name the same no need to edit /etc/fstab

You did it already... There is swapoff command. The computer may do some read/write on the swap so you Should turn it off before that. Unmount it, comment it in /etc/fstab, then do the same again with 1GB file. You have to be root or use sudo.