Many incandescent-only dimmers do not require a neutral wire. If that's the case then you will have hot, switched-hot and ground connected to the existing dimmer but not neutral. The new dimmer will likely require neutral. Neutral may be in the box in which case you have it easy. If not then it should be nearby and the challenge is to make sure that you have the correct neutral and bring it into the box, split it and pigtail to the neutral on the new dimmer. Code now requires neutral in all switch boxes but that has not always been the case.
The above is a general dimmer/smart switch/etc. issue.
Now for the specifics: Based on the UPC code of the package, this is a Lutron LECL-153PH-WH dimmer. I found the spec sheet for it and it explains the wiring. For a single switch (i.e., you have one dimmer switch controlling the lights and no secondary switch at the other side of the room):
- Hot (typically black) to black wire of dimmer.
- Red of dimmer to switched-hot (typically black or Harper's preference red)
- Green to ground (green, bare or screwed to grounded metal box)
- Red/white of dimmer capped - i.e., put a wire nut on it so that it isn't connected to anything.
The Red/white and Red are used together as travelers for a 3-way switch (2 switches controlling the same light).