Bluestacks App Player already comes tweaked and customized to run as fast as possible. You can adjust the memory using RegEdit and it's a simple process.
Firstly, go to Bluestacks App Player's installation folder and locate HD-Quit.exe. Launch it to close all the services and opened files.
Go to Start > Run > regedit and navigate to
HKEY_LOCAL_MACHINE\SOFTWARE\BlueStacks\Guests\Android and locate the Memory item. Double click it and switch to Decimal. Input 1027 then start Bluestacks App Play and it should run Faster.