There is a big difference between the memory allowed for Bluestacks and the physical memory available in your computer. Bluestacks requires 2 GB of physical memory to be able to run in your computer. Besides memory, it's recommended to have a dual-core computer and a power graphics card or your games will not run at all. You can change the allowed memory for Bluestacks from the registry using the following path:
HKEY_LOCAL_MACHINE\SOFTWARE\BlueStacks\Guests\Android. Double click the Memory string and select Decimal and give Bluestacks enough memory but up to and no more than half of the total memory available in your computer.