People worry about copyright issues. As far as we are concerned, Graham created these tutorial projects in order that you have a go at them. If you achieve pictures that you are happy with, then sign them as your own, frame them and exhibit them, then Graham will be delighted.
If you intend to sell them it is polite to sign after, under or near your own signature "after Graham Berry" or 'inspired by Graham Berry' If you like any of Graham's paintings and fancy 'having a go', please do. As soon as you sign a 'copied work' as your own it is always polite to acknowledge the original artist, otherwise you may be accused of "passing off" as someone else. All artists get ideas from the world around us, but to specifically copy another artists work should be acknowledged, all be it in a small way.
Enjoy your painting, we do hope Graham's work encourages you.