They've provided me with a file containing three strings of characters (33 characters, 66 characters, 52 characters). One the three strings starts with a K.
I'm assuming the 52 characters line is the string that starts with K and that the 33 characters starts with 1?
Go to your Electrum wallet, at the top left, go to Wallet>Private Keys> Sweep and key in your private key in this manner.
Afterwards, you should get a dialog that shows the transaction information, at the bottom left, there should be a slider that lets you adjust your fees. Depending on how long you want to wait, the current somewhat optimal is about 30satoshis/byte. Click Finalize, check again and then Sign and Broadcast.