Windows 7, 8, and 10 64-bit need a minimum of 8 GB to run decently - 16 GB for heavier loads. That exceeds the limit of memory for your machine.
The hard drive is likely 5400-rpm which will slow down the computer enormously under heavy load.
Since the machine is 12 years old, you need to consider a new and faster machine.
You can try upgrading the hard drive to an SSD and that will help if it will work with the older BIOS and computer. Still, I would hesitate investing money in this machine. Put it toward a new computer.