A tip from my recent experience - you might need to change the fan unit as well.
I changed the resistor pack for the same reason about a month ago, and within 2 days it failed again. Probably something was wrong with the fan, so I got a new fan and installed it. It runs a lot more smoothly and quietly than the old one.
Now I need to get another resistor pack...
I love the fact that it's only 2 easily accessible screws to get the resistor pack out, and only 3 easily accessible screws to get the fan unit out.
I had a similar problem in my wife's 2004 Renault Scenic, and there I had to dismantle the entire center dashboard and passenger side glovebox to get to the resistor pack...
And on the Scenic I also learned the hard way that just changing the failed part is not enough. The connector had burned out so I changed it, but it burned out again, and it turns out one needs to change the resistor pack to a new version as well to prevent the connector burning out again... I dread doing that job one more time...
The funny thing is that on the Scenic the fan doesn't work on 4, and in the Punto is only works on 4 - so between them I have a fully functioning fan