If RBF was not activated you could double spend it with a higher fee.

You would need to connect to an Electrum server which does not have your transaction in the mempool anymore (just try a few until your transaction does not show up in the history anymore) and create a second transaction with the same input(s) as with the first.

Edit: older bitcoind versions remove old transactions after 3 days, newer ones only after 14 days.