>>543113
Give it a 64/128GB SSD as others have suggested and don't invest a cent more on the system.
That SSD will keep on being useful while the rest of the system is on its way out and no other upgrade will justify the price anyway.
Install a very lightweight Linux distro (the most heavyweight you're looking at being Lubuntu or a lighter distro with XFCE) and that system will keep on being useful for a few years.