Unconfirmed transaction, how do I cancel this?

Hi I accidentally sent some coins without a transaction fee. They have been sitting unconfirmed for about a week. How do I cancel this transaction? I am using “litecoin version v0.8.7.5-beta” wallet. I have tried double sending the transaction with a fee but it just tells me I do not have the funds to make this transaction.

thank you

Upload the latest wallet. Right click on the transaction and cancel.