If all your contacts are available in your iCloud online address book, on your iPhone go to Settings > iCloud > Contacts > Turn Off.
You will be prompted to Keep on My iPhone or Delete From My iPhone all previously synced iCloud contacts. Select Delete from My iPhone.
Follow this by turning Contacts back on for over the air syncing with your iCloud account.
If your Mac is now running Mavericks, there is no longer an option to sync contacts direct with the Address Book on your Mac via the iTunes sync process.