To level up your arms, try lifting bananas, or pineapples, if you prefer.
Then, start running around as fast as you can. That'll level up your legs.
For your brain, start smashing it against walls until you're strong enough to smash a soda can.
If you want to level up your stomach, you need to do a lot of belly flops.
That should cover the basic things you want to level up. Come back when you're ready, and we can continue your training.