There are a couple possible ways to do this depending on which version of iOS you are using.
First, try going to Settings > Touch ID & Passcode or Settings > Passcode (depending on if you have an iPhone or iPad with Touch ID). Tap it, enter your passcode, then tap on Turn Passcode Off.
If that doesn't work open the Settings app on your iPad and select General. Then look for where it says "Passcode Lock". Tap on that and disable it. You also want to make sure the Simple Passcode is turned off. After that you can go back to the General screen where you might also want to switch Auto-Lock to Never.
Face ID users will not find a setting called Touch ID and should instead go to Settings > Face ID & Passcode. From there, swipe down until you see and can tap on the Turn Passcode Off option.