In general, as you can see on the picuture, the piece is sitting on two nodges (A and B), so you need to lift it first up a bit (C) and then in pull in direction D.
Normally the piece should slide out easily after a bit of pressure. If it does not slide out easily, then it usally means its corroded or there is some dirt there.
I suggest you try some rust remover or some other cleaning product.
If its stuck there due to dirt, you may use some wood piece to carefully hammer it upwards.