mdm, If you look at the picture you will see at the end of the rod there is a rectangular piece that looks like a "C clip" at the ends. On the forend metal there is are two notches where this piece fits into and when the button is pushed in it expands and releases itself on the barrel loop (lug). You still have to pull down on the wood to release the "J" spring also from the barrels loop.
The button only moves very slightly, just enough to spread the clip and release it from the loop.
First try pulling the button out, it is only going to move very slightly, if it does not pull out then hold down on the button and pull the forend off. Make sure gun is re-cocked any time you take the forend and barrels from the receiver.