Remove the furniture from the room and prepare the carpet by first vacuuming and then shampooing it. Vacuum all the dirt, dust and debris deep in the carpet fibers. Shampoo to remove the remaining dirt and any sticky messes.
Unroll the plastic strip and lay it against the bottom of the walls, securing the top of the plastic strip to the walls with painter's tape. Tuck the bottom of the plastic strips into the small crevice between the carpet and the wall. This protects the walls from carpet dye.
Prepare the carpet dye kit by mixing the liquid or powder dye with water, according to the package directions. Once mixed, carefully pour the mixture into a spray bottle.
Spray one, 2-foot-by-2-foot patch of carpeting at a time, starting at the furthest corner of the room. After spraying, scrub the carpet to push the dye down into the deepest fibers. Keep track of the number of sprays you use in each section to produce an evenly dispersed dye job.
Allow the newly dyed carpet to dry for several days, then shampoo the carpet again to remove excess dye before it transfers to your skin and clothing. Allow the dyed and shampooed carpet to dry completely before using the room.