Loosening them up isn't the issue. You are "brand new to guitar". I hate to break the news to you, if you wanted to be shredding by the end of the week, but it takes years to get proper hand posture in the muscle memory.
First off there is a natural curvature to the grip and that will not go away. How much of an issue this is depends on what you are trying to play, some guitarists play on the pad more than the tip and if you do that the bend of the fingers will not be as severe. Classical guitarists play more on the tip.
Ideally, as a beginner, you should be able to keep each of the 4 fingers over 4 consecutive frets on one string and play a chromatic sequence (1, 2, 3, 4) and (4, 3, 2, 1). You should also be able to pin the string down right behind the fret (not just anywhere within the space between the frets). Clearly this may require a bit of a shift as the middle and ring fingers tend to want to stay together.
Stretching is not the answer, focused practice on simple exercises like the 1-2-3-4 on all strings in different positions is the key. If you search you will find some place on the neck where you can do this fairly easily without a lot of stretching or other contortions. Practice there until it's comfortable and effortless, then start moving further back toward the nut and up towards the bridge.
Some of my students (with hands that look like yours) find it easy to do this exercise on the top 4 strings (D, G, B, e) up at the 7th fret but can't seem to get the A or E strings. After a couple weeks of practicing on the top strings the A and E worked no effort (it a form of tricking your body to accept what is difficult as being a small perturbation to something easy). Sometimes we focus more on the hardest thing and get nothing done. You want to train your fingers to be comfortable in proper position. They should float over the fret spaces even when one finger goes down to fret a note (many people cramp their hand together a lose form).
If you work at maintaining proper posture and nailing the correct note your hand will adjust. It is natural for the index and pinky fingers to hit the string slightly on outside rather than directly under the finger nail like the middle 2 fingers, so don't worry if you cannot get that to happen. Everyone has slight deviations in physiology and needs to adjust expectations, but forcing your body to do something contorted will not make your form better.