CPU: both are not upgradable as those are BGA (aka soldered CPUs), so you'll have to live with it.  At the very least they have 4 cores and 4 threads but they aren't not exactly a fast CPU to start with (it's essentially a fancier version of Atom CPUs)
RAM: both are upgradeable
HDD: both are upgraddeable

For best performance you should consider upgrading the RAM and the drive to a SSD

https://support.hp.com/my-en/product/hp-20-...ument/c04270503

Both AIOs support supports up to 8GB RAM (DDR3 SODIMMs) and a regular SATA SSD
I don't think you should run AutoCAD on such a low end machine, those CPUs are more or less designed for very lightweight use (even that kind of load is a huge task for those CPUs)

Usually those AIO computer the processor is not upgradable due to the processor was built-onto the motherboard.

What is AIO?

Ram are soldered. Only HDD can change

RAM and HDD can change 

The 2GB RAMs have been removed and replaced

Don't think there's any point in me keeping these 2GB Rams, what can I do with them besides tossing it away (which I very much prefer not too).