Yo, so ECO mode is honestly one of those things that trips people up because it depends on which JK you've got. If you're running a newer JK with the newer dash setup, you should see an "ECO" button right on your steering wheel controls – just tap that bad boy and it toggles off. Super simple.
Now, if you've got an older model, you might not have a dedicated button, but ECO mode can still be active depending on your transmission settings. On my JK, I found that putting it in Sport mode basically disables ECO and gives you more aggressive throttle response, which is what I wanted anyway when I'm wheeling.
The thing is, dude, ECO mode isn't really a problem for most people – it just dulls your throttle input to save fuel. But if you're doing heavy offroad stuff or towing, yeah, you want it off because the transmission will be happier with more direct control. Check your owner's manual for your specific year since the placement of controls can vary a bit year to year.
What year JK are we talking about? That'll help me give you more precise instructions. And are you just wanting it off all the time, or just when you're wheeling?