I want to do it without restoring it to factory settings

I want to do it without restoring it to factory settings

depends how you sync with iTunes. are you syncing all songs from your iTunes library to your iPhone? are you syncing a specific playlist.

in iTunes, click on your iphone when it's connected (on the left), then on music at the top and it gives you options for how you want to sync. you can sync only checked songs (in which case uncheck all the ones you don't want to Sync) or you can create a playlist which you can fill with songs that you want to have on your iPhone, then sync only that playlist.

Plug your Iphone into it's usb.
Connect to Itunes.
Select songs/albums you wish to delete
Right click
Select delete