How to keep songs I deleted off my iPhone?

I put on many songs onto my iPhone, but I realised I probably wouldn't listen to all of them. I deleted some from my iPhone, but not off of my computer's sync list. Then I downloaded some songs to my iTunes on my computer that I want to put onto my phone. Unfortunately, when I sync my phone and computer, all the songs I had previously deleted from the phone were put on again!
My question is, is there a way to keep my computer from adding any previously deleted songs to my phone?
(I have quite a few of them, so I'd rather not go one at a time.)

Hi, thats easy just go on the itunes store and click the last box and click purchases and press download
hope this helps:-)
-awesome

I've had this problem before. Connect your iPhone to iTunes. Click on your connected iPhone on iTunes. Scroll down on Summary to Manually Manage Music and Videos. Let it apply. Once it is done, a music tab should appear below your iPhone. Click on that and delete the songs you don't want. This should work.