I'm assuming you wan't to put upgrades intho that build instead o putting up a completely new one.
You have taken a look into the support website of the manufacturer?https://support.hp.com/us-en/document/c01896260
- The fastest CPUs would be either the Phenom II X4 980 or X6 1100T (It is shipped with a X4 945 with 95W TDP)
- The boards supports uo to 16 GB DDR3. That should not be a problem, as this is pretty decent even today.
- The case features 4 ull height slots on the back side, so graphics card size should not much of an issue.
- The system is shipped with a 300W ATX power supply. So that should also be not much of an issue.
- Good to know that HP is actually following the established ATX standards and form factors, that eases the upgrade process, ass nomrla off-the-shelf parts should fit.
About upgrade choices:
- Easiest would be a simple graphics card upgrade. Under the assumption that the PSU deliveres enouth power on the needed rails and the power draw of the CPU any PCIe graphics card with less than 150W should work without issues, although a card above 75W will need an additional plug that mght or might not existent on the power supply. If the 6-pin plug is missing, that woild be a strong indicator to get a new unit.
- The faster CPUs avaiable are sitting at 125-140W TDP, taht together with a strong graphics card (like a GTX 1050 Ti or RX 460, wouldn't suggest anything stronger as even the top CPUs supported on the board would still be a bottleneck. And with OEM boards overclocking is generally not an option) would clearly mean getting a new, decent power supply of the 450-600W range. Also as with other older platforms the top models aresually rather expensive, even used, as you'll be not the only one to look after them.
- Another good choice to speed up general tasking would be an SSD, the sweet spot currently lies in the 240-512 GB range.
In the end it depends on your budget.
Also building a new system might be an potion.
You could move over your drives. As the most recent platforms requirede DDR4 you wouldn't be able to keep your RAM, but getting a slightly older platform that supports DDR3 (Intel: SandyBridge - Skylake) might be an option.