If your electrum wallet is version 2.7.0 or newer, and you enabled Replace-By-Fee in its preferences, you can replace your transaction with one that has a higher fee. However, Replace-By-Fee is disabled when you install a wallet, you have to enable it yourself.
If it's not enabled, and you would like that option for speeding up future transactions, then enable it using the following steps.
Select tools, then preferences.
This is the default preferences window.
Check the "enable Replace-By-Fee" checkbox, then click the close button.
When you send Bitcoins check the checkbox marked "replaceable" to make a transaction that allows Replace-By-Fee.