While some Delta handle styles can offer clues, the most reliable method is to remove the handle and trim plate to visually inspect your existing cartridge. Note its color (gray or white) and any distinguishing markings or numbers to ensure you purchase the correct replacement part.

You'll primarily need slip-joint pliers or Channel Locks for gripping the bonnet nut and a Phillips head or flat head screwdriver for the handle and trim screws. While specialized tools are listed, basic versions of these are often sufficient. Ensure your chosen pliers can provide a secure grip without damaging plastic components.

First, check for an individual shut-off valve to your bathroom or shower, often found behind an access panel. If no such valve exists and the main shut-off is inaccessible or faulty, it's best to contact a professional plumber to avoid water damage and ensure a complete water stoppage before proceeding.

Double-check that the new cartridge is fully seated and properly oriented; the 'H' and 'C' markings usually align with the hot and cold lines. Ensure the bonnet nut is tightened securely, but not overtightened, and verify that all O-rings are in place and adequately lubricated with plumber's grease.