Thanks, here is info
Model WDC WD5000AAKX-08U6AA0
Thank you very much!
So this means you've got two slots (or at least that's what we're seeing) and in each of them you've got a 4 GB DDR3L memory stick running at 1333 MHz. Note that DDR3 may not always be compatible with DDR3L due to the fact DDR3 runs at 1.5 Volts and DDR3L - 1.35 Volts. This means that if you decide to upgrade the memory and buy one 8 GB DDR3L stick at 1333 MHz, you'd have to remove one of the 4 GB sticks and you'll be left with 12 GB RAM. You can always get two 8 GB DDR3L sticks and end up with 16 GB RAM, but is it really worth it?
You have got a 500 GB Western Digital Hard Drive running at 7200 RPM. Now, Windows 10 runs very slowly on Hard Drives and it would really make a big difference if you install it on an SSD. However, that would mean having to transfer all your files, install all your software over again and set up the particular settings of particular programs and software again once more. That would also mean using a new Windows 10 license.
You can possibly upgrade the CPU too. Perhaps to a Core i7-4790 or another Haswell Processor, but there always exists the possibility it may not work or that you'd have to think about getting a better cooling solution.
Getting an SSD and installing Windows again on it would really speed up the system. So would getting a new Processor. But, if you ask me, it would be best to upgrade nothing and to keep the hardware in its current state, because there really is a chance something might not work or end up being fully compatible, in which case you'd need to spend even more money to send the machine to the repair service.
Now, I'm almost sure the CPU upgrade will work. But almost does not mean 100%. I am also sure that getting an SSD would really speed things up, but keeping in mind you'll lose all your files and settings, I don't think you would like that. A memory upgrade would be welcome too, yet I think the SSD would bring-in more performance.
So, in the end, it may be good to try and optimize performance on the current machine via software instead of upgrading it. You can try to upgrade it, but this is a Warning that things may go askew. Everything works now. So an upgrade would be necessary only if you're completely familiar with the process and have another computer you can use if something with the desktop goes wrong.
In the end, my two cents is to keep things as they are unless you're really sure you want to upgrade and prepared to face any unpleasant consequences should they arise.