How do you erase certain parts of the memory?

[MulleDK19]

I, personally, find it hard to believe that you can just...snap your fingers and make someone forget something. The human brain is just too complex for that kind of thing. We are not like computers where you can just go to the Recycle Bin and hit "empty". I honestly don't care if hypnosis is real or not...but the manipulation of one's memories through repetitive hand waving and saying "You will forget having played the game Penumbra!" is just impossible...unless someone can tell me exactly how it works.

EDIT: I'm not trying to be a pain in the neck or piss anyone off. I just want someone to definitively explain to me how it works.

The subconscious is the part of your mind that controls your feelings, thoughts and actions.

Hypnosis is a relaxation state, pretty much like REM-sleep, and a hypnotist is able to bypass the critical factor, by which he can gain access to your subconscious.

While under hypnosis you become susceptible to suggestions, and the subconscious is very powerful.

The subconscious is in fact so powerful, that you could be told that your hand is burning, and you would instantly feel an insane pain.

It's also a fact that we all undergo hypnosis averagely 7 times a day, and we all experience hypnotic phenomena all the time.

Like amnesia. For example, if you hum or hear a song, or seen a person but do not remember his name. You know you're supposed to remember, and it's as if it's at the tip of your tongue, but you can not get it out.

A hypnotist is able to create these phenomenas through hypnosis.