Where do I start on fixing the worst ATV ever?

I got this chinese ATV eight years ago, when I was a kid. And i'm still using it up to this day, although i'm probably going to ditch this one next year and buy myself a way better one; like the Banshee.

My atv is the actual worst. It was gifted to me as a kid from 'Santa Claus', a week later, I invited my cousins over to ride on it. They ditched in the canal behind my house, and had to end up replacing the carburetor etc. Fished everything out of the canal with our Ford. I remember all my family members tweeting about it on their phone, and me crying because I thought it 'died'.

It's a ($900?) ATV, Chinese, it's four stroke. It's supposed to go 44 MPH, only hitting about 20-ish. That's somewhat expected, considering it's survived being submerged in water and eight years of constant usage, but I've never really replaced anything besides the ignition and the carburetor. The chain is all rusty and i'm sure a lot of parts are on there too. All being set aside, I do want to fix it up a bit just so it can be running better until I get a new ATV next year. I'm pretty new to modifying vehicles, I usually just get stock and leave it like that, but i'm pretty sure at this point, it's a walking trash can.

Sounds like you got your money's worth out of this machine and have enjoyed riding it into the ground. No sense pouring $$ into it. Doubtful you will get anything for a trade in. Considering you could walk out of any ATV dealership with a nice, new 2019 model and a $130 monthly payment… Every cent you drop into this is money down the drain.

Fix the main shaft connected to the carb. It makes quite a difference. I gained 10 more mph doing that trick
I learned from a atv racer. A new self absorbent clutch cable will be second.