It depends on what you think you want to upgrade.
If the computer still runs , I might think about throwing a Different operating system on there Like a free Linux Distro ,
A lot of folks went to Linux after support ended for Windows XP .
My grandma has currently been using an old Windows XP computer for Gmail (pretty much all she does online) and the computer is in dire need of an upgrade. I was thinking an ASUS Chromebox or maybe even a Raspberry Pi. She prefers a desktop-style form factor and not a laptop or tablet. Needs to be very simple, secure, self-updating, etc. I welcome suggestions.