Send a letter to the Microsoft head office of the country you're in detailing what happened, what losses you suffered and the amount of compensation you're seeking. If you're in the UK then send the letter using Royal Mails' "Signed For" service. If you don't have any luck with that approach then try the Small Claims court.
However, because computers are such complicated systems you're going to have real difficulty in proving that it was the Microsoft update that wrecked your computer. Microsoft could easily argue that a third-party app interfered with the update process, or perhaps a faulty hard drive, or perhaps zillions of other things were to blame.
By all means pursue this but your chances of a good result are slim.
Before you contemplate any form of legal action, you should be aware that when you used Windows for the first time, you accepted the terms of the Microsoft End User License Agreement (EULA).
That agreement limits the amount you may recover in a legal action to the amount you paid for the software, or - in the case of a free installation of Windows 10 - to US $50.
In order to initiate a claim for consequential loss, you will have to provide proof of your loss. You will also have to produce evidence to show that you contacted Microsoft and allowed them at least 60 days to remedy the problem.
It will be very hard for you to prove loss - the update you mention has almost certainly not 'destroyed' your computer. In the 18 years I have been involved with this forum I have not seen a single provable case of a Windows update destroying a computer.
If you would like to engage with us in an attempt to rectify the problem, tell us exactly what you have tried so far in terms of getting the machine started, and we'll offer suggestions. Nine times out of ten we are successful.
Otherwise, write to Microsoft:-
Microsoft Ireland Operations Limited, Customer Care Centre, Atrium Building Block B, Carmanhall Road, Sandyford Industrial Estate, Dublin 18, Ireland
Tell them what has happened, and tell them who you spoke to at Microsoft and when, and tell them what advice you were given. Keep a note of any calls with date, time, and name of the person you spoke to. If you intend to pursue a claim for damages, start gathering proof of your financial loss. You will get nowhere in a court unless you can produce that evidence.
Pretty sure the End User License Agreement (EULA) protects them from virtually any complaint you can think of. It's unlikely that a Windows update gone awry will get you anywhere legally, unless your country has dramatically different laws than mine (USA).
It's not really fair to suggest that simply because a person hasn't responded, he or she is 'simply wasting time'. That's not we're about here.
It's great that so many people give freely of their time to help others, but we shouldn't expect a thank you, or even an acknowledgement that our advice worked (although it's always nice when it happens).
Lots of people get the answer they are looking for, and just move on - that's life, and over the years we've seen it thousands of times.