when i delete song on iphone then sync it with itune it comes back on iphone . way you can stop this and delete song completely

Assuming you have checked "sync only checked songs and videos" on the Summary tab of your iTunes sync settings, uncheck the songs you don't want on your phone in iTunes before you sync and they will not be transferred back to your phone when you sync.

Thank you. That solves that problem. Two other questions I have: How do I convert songs from 256 mbps to 128? When I convert them does it lower the quality significantly?

You're welcome.  To downconvert a song you would probably have to re-import it after changing your import settings in iTunes.  If you go to iTunes>Preferences, on the General tab about two-thirds of the way down click on Import Settings, then change the setting to Import Using AAC Encoder and Using High Quality, it will then rip your CDs to 128 kbps.  Then delete the 256 kbps songs from your library and re-import the CD.

I'm probably the wrong person to ask about how significantly this degrades quality as I have some hearing loss and probably couldn't hear the differences someone else might hear.  Gues you could try this on a couple of songs and decide if you feel it is a significant change or not.