Complete removal isn't possible without either oblivation or drug use, and I don't recommend either. You can try to reassociate those memories. For example, you saw a band in concert with this former friend. Don't focus on who you were there with. Focus on the life experience that you now have. You have a story to tell now that you wouldn't without the memory, which has made you a more full and complete person.
In time, memories will fade. The hurt will as well, but that is your present focus. Put your energy towards other things than your dark feelings; you will swim past your unhappiness the sooner you are able to stop treading in its waters.