I tried to put bitcoins into an p2p exchange with bitcoin-qt. I added a to small transaction fee, so the coins are now stuck as "Unconfirmed". The offer from the exchange is overdue, so all that will happen if the transaction gets confirmed is that I get them back with an administrative fee.
I would like my coins right now and avoid paying the fee. I've read that you can double spend the coins back to yourself and if I add a higher payment fee than the first time this would probably override the original payment. How can I practically do this? I'm not a hardcore developer but feel comfortable using commandlines and know my way around computers.