It's pretty basic for me. I go "into" the memory (that is, recall it as vividly as I can, including any and all emotion, sight, sound, even smell, whatever is available), and from there, I see it as a sort of "stage set" built out of energy, and I know that I created it, myself, and that I can uncreate it. I then stand in the middle of it (so to speak) and consciously and deliberately "deflate" it by withdrawing my energy from it. Eventually, it collapses, and after that, it's not a problem.
Some memories are so potent that it takes more than one session to completely deflate them (many of my traumatic memories were like this). And I don't always go "into" them. For some things, I can just get a fix on it in my awareness and suck the energy out of it without having to build the entire scene.
I'm sure other people can think of other ways to do it. This is just the way I generally do it. I could probably think of other ways, too, but this works, so I stick with it. I will say that, like anything else, the more you practice it, the easier it becomes.