Remove Floor mats
See  Floor Mat removal

NOTE: The view is for the left side, right side is the same

Remove 4 Bolts

Slowly Pull the rail towards the back and out towards you

This what you will have

Installation

Reverse to install

Holes #1 & #4 are open and #2 & #3 Have Threads for the bolts

The front is interlocking
Slide them together while pushing the rail under the floor panel