My drawer slides were installed at the very bottom of the drawer box so these instructions are for installing new ones in the same position. If yours were installed higher up on the box, use the existing screw holes from the old slides to position the new ones.
Again, use the oval slots (the ones that are up & down, not side to side) and use two screws for the middle and back of the box. A screw is also inserted in the round circle at the front of the box when you have positioned and secured the other two screws.
Pull the center portion of the drawer slides inside the cabinet out so you can slip the drawer box slides into them.
Push the drawer firmly back into the cabinet – it will be a bit stiff. Pull the drawer out again and it will glide beautifully! If you have installed the slides too close to the front of the cabinet, you can partially unscrew the drawer box slides and reposition them because you used the oval slots that allow you some maneuvering room. If your drawer is too high or too low, you can adjust the slides on the drawer sides using the up & down oval slots. If worse comes to worse, you can re-drill the holes to get your spacing right. The first drawer is the worst, once you get it done right you know how to approach the rest.