Stairs are a high-traffic foot area, which means the carpet will wear down faster than other spots. Replace your stair carpet by following these steps (no pun intended).
Start by removing your old and worn-out stair carpet including the padding underneath. Check your stairs for any structural damage and repair any broken risers or steps.
Pre-cut your carpet to fit the width and length of the carpet needed to cover the stairs. It's fine to go in sections, but don't underestimate how much carpet you will need.
Apply carpet padding to each step using a hammer stapler. Keep the padding taut and staple around the edges and through the middle of the padding to secure it to the stairs.
Evaluate the condition of the existing carpet tack strips. These are the wooden strips with sharp tacks pointing up that grab the carpet. If they are in good condition and not water damaged, then they can be reused.
Install your pre-cut stair carpet starting from the bottom stair and work your way up.
Use the aptly named stair tool to tuck the bottom of the carpet below the first step, then use a knee kicker to tighten the carpet across the step. After the carpet is tight, a pneumatic staple gun should be used to tack it into place. Repeat this process for each step and you'll have a newly carpeted staircase before you know it.
How to Install Carpet on Stairs [Showmethefloor (YouTube)]