How Can I Increase My Usable Ram To 4Gb In Windows 7

ControlPanel >System shows that: Installed Memory(RAM) 4.00 GB (2.53 GB usable).

I found some patches for Windows 7 and applied them to my system and now it shows this : Installed Memory(RAM) 4.00 GB(3.87 GB usable)

I want to know is there any solution for get 4.00 GB usable in Windows 7 32bit?