Well, I forgot the details but basically what u gotta do is to get a special tool - called something like fork splitter - at least it does look like one. U gotta place the tool between the armrest and the seat itself, and kinda pry it towards you; the armrest is gonna pop out.
Now, if you wanna put the armrest back - u gotta first heat up the white plastic ring that's attached to the armrest; otherwise it would be close to impossible to put it back.
I did it myself - with the above mentioned tool it's a piece of cake. Better off get some cool aftermarket seats