Easy and quality might be two different things. I will explain some of the easier ways of stripping deck railings with the last explanation being the most time consuming. The best choice for you depends on the condition of the rails and the deck stain.
1) Power Washing – You could just wash the railings along with the rest of the deck before staining. This is the easiest and fastest way.
2) Simple Washing With a Deck Stripper – Many wood deck strippers are on the market. Most work well, but could harm plants that are around your deck. Choose a deck stripper that is environmentally friendly and states "Will Not Harm Plants" on the label.
Many strippers will remove semi-transparent deck stains and some solid colored stains. They will have a difficult time removing paint.
3) Deck Stripper and Sanding – This involves using the stripper to remove as much of the old stain/paint as possible then finishing with a light or medium sanding. This will produce smooth surfaces on the railings and most of the stain or paint will be gone.
4) All Sanding – This is the most difficult and time consuming way, but produces the best results. Most appropriate for very difficult stains or paints that are peeling.