First, backup all the files you want to keep.
Unless you have a separate computer as your main Windows environment, it is probably a good idea to make it a dual-boot system. This means you will have an option to choose Windows or Linux when your computer boots up.
There are a bajillion Linux distribututions to choose from. For a non-geek with no special needs from the OS, I recommend Linux Mint.
There are installation instructions on that site that will guide you through the process.
Here is a summary of the steps:
1. Download an ISO file. Linux Mint has three variations: Cinnamon, MATE, and Xfce. I prefer MATE. If I'm installing to an underpowered machine, I use Xfce. If you have experience using a Torrent client, it will benefit you here as it will decrease the time it takes to download.
2. Verify the ISO file. This makes sure the downloaded file wasn't corrupted in transit, and that it is 100% entact and exact.
3. Download, install, and use Etcher to copy the ISO to a USB drive and make it bootable.
4. Find out what you have to do to get your computer to boot to the USB Drive before booting from its internal drive. When your computer starts, you can hold down a key to open your BIOS menu. Be cautious about changes you make here. If you're not sure what a setting is for, don't change it before learning what it does. In some cases, you will have to remove protections, and someof those can only be changed when other features are off/on, etc. Sometimes the boot order is easy to find, and easy to change. Set the boot order so the USB drive is before the internal drive, and save the changes. After Linux is installed, you can set this back to boot from your internal drive first.
5. Once you're able to boot to Linux from the USB drive, the rest is a piece of cake. I recommend running Linux from the USB drive before doing any installation. You may not have every feature working, but all the major stuff (keyboard, monitor, wifi, and mouse) should be working. If not, some troubleshooting may be required, but I've never experienced, or heard of, this happening. After this smoke test, click the icon to install, or reboot and choose the install option.
6. The installer will help you partition your drive. You can allocate as much or as little as you want to either side (Windows vs Linix). You'll select language, keyboard, timezone, username, and password. MEMORIZE OR WRITE IT DOWN! If you can't remember your password, you'll be screwed. That's security though.
7. After the initial install, there will be updates. Once complete, play around! The settings for the UI, etc need an overhaul in terms of organization, but with some exploring, you should be able to change most aspects of the interface.