I wouldn't tell anyone.
I would wait a couple of months and then give my nearest and dearest a meaningful chunk each, enough to massively improve their lives and obliterate worry, and tell them I had won a much smaller amount and distributed it all amongst us.
These amounts would be enough to buy all nieces and nephews a flat each, create a really good pension fund for older relatives, but some a small house each etc or enough to upgrade to a 'forever' house.
I would complete a building project that a charity dear to my heart needs, and make a significant donation to a charity that has helped one of my Dc.
I would set up an endowment fund to support a specific range of training courses in my industry and in my local area.
Buy a few properties - one specific one, for my wider family's use as it is our favourite place, and a town house and a country / coastal retreat for me. I would let other people use them, they wouldn't stand empty.
My DC would get Uni costs, enough for a flat, and money in trust for a later house, a car every 5 years, and a fund for establishing a business or undergoing training. I wouldn't just bung them a massive load of cash in one go.
I would get out there and enjoy my life - give up work, go to galleries, go camping, go on long walks (The Lycian Way etc) , not a blingy champagne soaked lifestyle. I wouldn't buy an expensive car, for example. I really don't want one.