How to replace the keyboard of the Lenovo Ideapad 320S - 14IKB laptop

This Lenovo Ideapad 320S laptop is over 4 years old and it's a quite a good laptop for its age, but in time the keyboard became so messed up that I literally can't use it anymore, with some keys sticky and other completely broken.
Not to mention my trial to stick fluorescent keys on top of it which seemed a good idea at the time, as they help a bit in the dark, but they also got very ugly in the end.
So I postponed the keyboard replacement until literally the CTRL and Space keys didn't respond anymore, when I had to do this operation.
As you can see, even though I am a jack-of-all-trades, I didn't replace a laptop keyboard in ages, which is visible in the video... :)
Still, it worked out ok eventually and now I have a lovely and WORKING brand new keyboard, so I thought to share the procedure so others benefit too.