I see two completely different questions that have two completely different answers:
1) Change your life. That would have to be enough money for you to not have to work again, ever. You might choose to work, but whatever work you do would be by choice rather than for money.
2) Improve your current life, but you have to continue working. That would be a much smaller amount.
For me (1) would be at least £5M and upwards. There would be changes from £5M to £100M, maybe further. (2) could be as low as £20K. Clear my remaining bit of mortgage, buy a few home improvements. There would be further improvements with more money, e.g. enough to provide an income of even a few thousand a year would allow me to reduce the hours I work, which would significantly improve my life.
But as it is, I'm doing OK now. Thank goodness I was able to buy a house >20 years ago. I don't even know how people manage nowadays. Renting a single room costs more than my mortgage.