Battery will wear out after a while. The only thing you can try is emptying it completely and then charging it without using the laptop at the same time, once it's fully charged from fully empty, it should show the maximum stamina it can, which still definitely won't be 4 hours.
Like Vershel said, the screen uses most power on your Laptop. Once you put out the power plug, it usually automatically sets itself onto battery mode(usually slightly less powerful mode with less contrast). Try lowering the contrast.
The more power you use(running games, movies, internet, some programs) the less the battery will last. If you have Wifi or Bluetooth or IR or anything of that kind on, that will consume extra power.
Some Operating Systems will consume more power than others! For example, Windows 7 is suspected to use up more battery than Windows XP, so if you have 7 on your laptop, try installing XP for some extra stamina.