This tutorial is for those times when you need the lines in your photo to be straight and square. It'll be most useful to real estate photographers, but everyone has a problem with lines from time to time.
Apology: I don't know how this method works if you use Lightroom in conjunction with Elements, sorry. But Lightroom has its own distortion controls in the "Lens Correction" tab, so try those and see if they give you sufficient control.
Step 1: Open
Process your raw file in ACR in the usual manner, then press "Open Image" to bring it into Elements.
(Distortion is like Liquify - it must be done as the very first step in your Photoshop editing workflow, immediately after your raw editing, before any layer work.)