How can i make inner thighs more straight?

My inner thighs appear to lack size and they kind of curve inside. How can i get inner legs like this?

Leg press, Front Squat, Sumo Squat, and weighted lunges should all help there. Foot position and stance is the beigger part of what area will be worked even in those exercises. I would use a wider stance with toes pointed out being sure to push off on more of the front/toe end of the foot. Practice good contractions in that muscle group and be sure when you lift looking to build those areas squeeze from those muscles during the lift. I know this is what has helped me grow my inner thigh.

The adductors are the muscle you want to stimulate on the inner thigh. As Mindmuscle said, wide stance, toes out will help to hit the adductors. Wide stance squat worked well for me.