How do you change your mindset?

I’d like this to become a general discussion as well just to share experiences and such!

However, for context, I’ve noticed In the past 2 years I’ve become increasingly more negative in my mindset toward everything. I used to be a really, stupidly happy person, so much so I used to feel euphoric out of nowhere for no reason or for small reasons.

I’m really not sure what changed, if it was me just growing up and this is part of it. Or me changing as a person or my environment became more negative (I do think it might be this). However, I really need to change this and I’m a big believer in your mindset and approach are so important in how your life works out.

So any advice in radically changing your mindset to a more positive and happy attitude?