Just received a secondhand iPad and want to change the iCloud account name

If it wasn't cleared when you bought it, take it back to where you bought it from and have them to it or have them give your your money back.

What you're experiencing is the activation lock, and it's meant to be a theft deterrent device by requiring the person that set up the iPad to clear away their iCloud info before selling it - and meaning if the device is lost or stolen it can't be wiped by the finder. As such, there is no way to user bypass it.

If your iPad will only show you a screen like this:

then it's Activation Locked as described above and only the previous owner can unlock it, either by providing you with the account ID and password, or by removing it from his list of devices (as he should have done before selling it) - please see http://support.apple.com/kb/ts4515

If you are actually able to get into the iPad and go to Settings, select iCloud and click 'Delete Account'.

You may be in the same bind. If you erase and reset the phone you will probably run into the screen I posted above, and be permanently locked out unless you can contact the previous owner. This will also presumably happen if you upgrade the system. You should take it back to where you bought it from.