Simply find your current wallet file (http://docs.electrum.org/en/latest/faq.html#where-is-my-wallet-file-located), and rename it to "OLD_WALLET_DO_NOT_USE" or something equally obvious
Or better yet, rename it and move it OUT of the Electrum wallet directory.Then install the latest version of Electrum, and regenerate your wallet using your old seed (File -> New\Restore -> Standard Wallet -> I already have a seed). As the transaction was never broadcast, it can't exist in your new wallet
. Assuming that is the problem, now I am worried that as soon as I update to the newest version of Electum, my transaction will go through. Will this happen? and is there anyway to stop it before I upgrade?