I have a transaction made from mycelium not confirmed from 2 days now, i'd like to double spend it whit a higher fee to complete the payment, it's easy to do this?
You cannot double spend in mycelium, the mycelium client won't let you.
You have to either wait for the transaction to be confirmed or wait that mycelium drops your transaction if it doesn't get confirmed in some time. Sorry I don't know how long is before mycelium drops the transaction if unconfirmed.
he could, however, export the public keys and import them into a wallet that would allow him to create a double-spend transaction. based on the situation, this is likely to be faster than waiting for the transaction to confirm on its own.
Yes, you are right, thanks. He can very well do this and speed up the process.