is pretty easy.
If its a brand name system go to crucial.com or kingston.com and look up the brand name/model name of your computer. They should have the info as to what type of Ram your system uses and how much Ram your system motherboard can support as well as how many slots are available on your system motherboard.
If its a generic PC you'll have to look up the brand name/ model name of the motherboard it uses to get that same info. I usually go to the motherboard manufacturers website for that info.
Memory prices can vary widely. I've upgraded a few systems recently with a brand of memory named "Timetec" that has worked fine. It's fairly cheap. I found it on Amazon. If you haven't switched Ram before just watch a few You Tube videos in advance. Its not hard to do.
If you decide to give Linux a try bear in mind there are hundreds of different versions (distributions) out there. They are mostly all free to download and install. If you find one you like you can donate to whichever one you end up using. One I have found works well for most new to Linux users coming from Windows is called "Linux Mint". (the Cinnamon version)
https://distrowatch.com/table.php?distribution=mint
That site lists most of the versions available.
https://distrowatch.com
Linux Mint just recently released their newest version. The download comes in a .iso file which can be burned to a CD or DVD depending upon the size of the .iso file using your computers cd/dvd burning software. Once you've created the disc you go into the computers "bios" and set the boot to start from the cd/dvd drive, save the setting and restart the system with the disc in the drive. The disc will have an installer application on it that allows you to set up Linux on your computer. As well the disc will allow you to explore Linux right from the cd/dvd disc before installing so you can get an idea of how it looks and works. Firefox and Thunderbird are available for Linux and look much the same as what you're using in Windows.
Anyway, as an old computer geek friend of mine who is no longer with us used to say about playing with computers..."Have fun wrecking science!".
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