Take the wheel to your LBS. They will measure the spoke lengths and order you the spokes.
Changing a set of spokes in a wheel can be done three ways. The short method is let your LBS do it. The other short method is do it yourself by snipping all the old spokes and building the wheel to text book. The longer way is replace one spoke at a time, re-truing the wheel as you go.
The third method you can do with the wheel in the bike and does not require a dishing tool.
The only tools you need are combo pliers and a spoke key.