If you've decided to upgrade your iPad and gift, sell, or otherwise pass along the old one, you'll want to make sure you delete all of your data first. A factory reset will erase content and settings on your iPad, leaving it (almost) as good as new for someone else to use.
Note that before you do a factory reset on your iPad, you should back up your device so you have a copy of your data to transfer to your new iPad or otherwise be able to access in the future.
Apple has step-by-step guides for backing up to iCloud or your computer, or you can transfer your data directly to a new device. The easiest option is to use Apple's Quick Start process when you set up your new iPad, but if you don't have the new device handy or simply want a backup for later, you can use iCloud or a Mac or PC to store your data instead.
How to reset your iPad
Once you've backed up your device so you can restore your data to a new iPad or access it later, go to Settings > General > Transfer or Reset iPad and tap Erase All Content and Settings. If prompted, enter your passcode or Apple ID password. You'll see what will be removed from your iPad, then press Continue to confirm you want to erase your device.
It may take a few minutes to complete the process, but once done, your device is wiped and ready to move on to its next owner.
A final reminder: returning your iPad to factory settings will erase everything, so don't forget to back up or transfer any data you may need before starting the reset process.