Switching formulas?

My baby will be four weeks old tomorrow. I've had her on enfamil gentlease for about 3 weeks. As I only could breast feed for a week. Anyways since being on this formula her poop is way thicker and green. I read online everywhere that this is normal when they consume this formula but it still makes me uneasy. Enfamil sent me a lot of samples and I have 6 ready to use bottle samples of the 'enfamil newborn' and I feel like it would be a waste not to use them. Plus im thinking maybe it will help her poop situation since sometimes I believe it's constipation. should I try giving her these tonight and see how she does? Or should I just continue giving her the gentlease?