How to delete songs from my iphone on my laptop?

Okay so I don't like any of my old music on my phone and I just went out and bought cds and downloaded them to my iTunes… But now I want delete all my old music on my iphone and put the new stuff on… How can I do that? Oh and also some of the songs didn't download right and so I can't listen to them and they are like a very light grey color. And I can't do anything with it.

Step 1: Open iTunes and connect your iphone.

Step 2: Click on your iPhone on the right hand side of the window.
On the top of itunes you will see a horizontal menu that says summary, info, apps, etc.click "on this iphone".

Step 3: You'll see your music appear, press Command or control (depending if your on a pc or mac) and a so control + a then hit delete.

Step 4: Reinsert the discs that have the greyed out songs and re-rip them to your itunes library deleting the old ones that don't work.

Step 5: Go back to your itunes library and select the songs you want on your iphone and drag them to the little box that says iphone.

Itunes