IPS 1: To get the two shelves stacked, remove (Twist around and pull) the 4 rubber feet of the top shelf first.
TIPS 2: To comfirm whether the shelves fit in your cabinet or not, please check the dimensinos below. You can also check the 4th product image to get more details about dimensions.
Top shelf: 16 x 8.9 x 5.7 inches (Width x Depth x Height)
Bottom shelf: 16 x 8.7 x 5.3 inches (Width x Depth x Height)