Path of Exile performance
Solution 1:
A possibility is trying to clean up your pc (e.g. deleting old/temporary files, disk defragmentation...) but I think that doesn't affect the games performance that much. Also check if you have installed the best driver for your hardware.
Nevertheless, if you already lowered all settings and still have lags you really should consider to upgrade your system :). If the hardware below the software is too weak to handle it, there's no chance of getting the game to work properly.
Solution 2:
If you don't mind having really poor graphics, you can try using the "dynamic resolution" setting, assuming you haven't already. It will try to hit the specified FPS (say, 30), by automatically reducing the resolution.
There are instances where you might have the impression of playing a 8-bit game, but it could be your best chance until you manage to upgrade your system.
Solution 3:
You need a new computer.
The hardware you're describing is roughly 10 years old, and was a budget build even then. It's completely unsuitable for running any modern games.