Of these songs, I would say Lady in Red is the toughest (for me at least) because of the range of notes.
One advice: sit at the keyboard and determine which are the lowest and highest notes you can sing comfortably by playing them on the kb as you sing. Then you can more readily pick songs that fall within those notes, bearing in mind that you may well have to adjust the key to fit your range.
Then, as the guys said, practice. Start with songs you know well and don't have to really work to learn the melody lines. As you progress it gets easier and easier to extend your repertoire.
I started singing because the singer didn't show up one night and I wanted to get paid.
But I had been practicing at home with a tape recorder for a long time.
The tendency starting out is to enhance your voice with effects, and that isn't all bad to a degree,as it can give you confidence. But be sure you are enhancing it, not hiding it.
Good luck,
DonM www.donmasonmusic.com