Such an interesting question, because now I have to decide if I want to continue with this type of existence, or completely change it.
I'll just have a really long vacation in my own world, the only one, free from disgusting creatures and nonsense. That's what I would do, I might create a good/decent/near perfect friend to play sports/games with.
But assuming I wanted to "fix the Earth/humanity" without touching anything else, it would have to be a monumental change. Just due to human anatomy & available resources, cruelty, pain and sadness would be deeply rooted in what means to be alive.
Without going overboard and making it a literal heaven (because that's an easy answer), I'd increase empathy levels in creatures to a
maximum degree, I'd fix the atrocious results of evolution (making bodies naturally strong and not prone to disease, malformations, extreme senescence, senses deterioration, etc), and I'd give to the planet near miraculous alchemical structures for prosperity (e.g: special plants that regenerate and don't die, easy to grow, that take matter and efficiently transform in fully nutritious fruits of all tastes and variations, appealing to all lifeforms (and including microscopic food), with near perfect nutritional value). I'd make outer-space less hostile, or at least planet Earth more resistant and the sun far less volatile.
On top of it, I'd give humans actual critical thinking.
This situation would heavily encourage humans (due to extreme empathy) help each other out, critical thinking to most likely behave logically & altruistically (because of the previous), and because of the resources, no great incentive to screw each other up, which would already be difficult due to what I mentioned. On the few instances of criminal & heinous activity, it would be heavily but appropriately punished, as being altruistic for the right cause does not mean being a soft, placating, exploitable weakling.
So in essence intelligence, empathy, strength/health, and resources for a big step in the right direction.