What version iOS is on the old ipad?
If your are using at least 5.1.1, you can back up old ipad to icloud, then restore new ipad from that backup.
Then you can restore the old ipad as 'new', and that will delete all data. If icloud is not available, you'll have to do it through itunes on a computer.
How to back up and restore (iCloud and iTunes)
About iOS backups
Sync your old one, set it aside
plug your new one into the same computer and follow the on screen prompts.
You will be given a choice to set it up as new or restore it from a backup of your old one. Choose that and the data off your old one will be put onto your new one, making it a near clone of the old one. You will just need to set up wifi and enter passwords for sites, etc.
Once you are satisfied that all your data is on the new one, on your old iPad navigate to settings and 'erase all content and settings'. that will restore your device to 'out of box' state and you can then sell it.
Well, i just changed from the new iPad to the newly released iPad Air, and i got all my data from my old iPad to the new one with the help of iPubsoft iPad to Computer Transfer, which is a good helper for the transfering of iPad data, including music, photos, movies, and so on! So if you want to transfer data from old iPad to new iPad Air, it will be a good choice!