What upgrade do i do to speed up my old desktop pc and laptop ?

Most Importantly, Upgrade your HDD to SSD. SSD is theoretically 12 times faster than a normal HDD and when you replace HDD with SSD the workflow of your system speeds up by say around 3 times. So your same configuration will work like a next level machine, i3 will work like an i5 machine.

You may use such HDD externally on USB port using a Casing OR you may add it back in your desktop or laptop as secondary storage disk. You may use the DVD Drive Space in a Laptop to do so.

Secondly, Add more memory Stick, giving larger table space to your virtual desktop will enable it to handle files and operations in a more fluid manner and you will notice an improved performance.

Thirdly, Get it serviced. Dust is poison for your chips inside. Removing them will increase your machines life and keep it cooler and more efficient. Add Thermal Paste to your CPU and make it Cooler.

Lastly, Fragment Files your Disks, Remove old unwanted and temporary files and do away with unused programs to free up space and make then work better internally.