I have a way it needs a new Text Document just create a new text document open it up type in
-availablevidmem 8 <-- put it in the text now close it up now rename it commandline now put in

C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto IV

now you have more memory

Something new if increase the number like say 55 or 25 or 10 it give you more memeory but be carefle if you increase the number to to high it can crash you game depending on your computers performanceit leds to Fatal Error RESC10 (RESC 10) ok good thats all i have to say