One of the best bang for buck upgrades you can do to a PC is to add an M.2 hard drive to run your operating system on, [insert statistics vs ssd sata drives and sata mechanical drives] the extra speed that an M.2 hard drive gives you will help you boost the performance of your PC, It’s a win-win as (more often than not) it’s an addition rather than an upgrade as you can hold on to your existing hard drive for all your games and files and use the much faster M.2 hard drive to run windows on(and one or two of your more demanding games), giving you a faster boot-up time for windows and faster loading times for games and other apps too. So easy to install, all you need to do is check that your motherboard has an M.2 slot.[Global block Win m.2 harddrive that will be big enough for your OS (operating system) and games]
Then assuming you have Formated your new drive, download the windows installation media https://support.microsoft.com/en-us/windows/create-installation-media-for-windows-99a58364-8c02-206f-aa6f-40c3b507420d
Make an install CD or usb stick and you're away (make sure you have access to another pc/laptop or at the very least a smartphone in case you run into glitches in the installation process)
And that's it, you'll be amazed at how fast your pc will now be running, Mine now boots up so fast, that it's sitting at the windows login before my monitor has even woken up! I am so happy with how fast my PC is running now, It was like getting a CPU and Ram upgrade for the price of a hard drive.