Yes, they will stretch out over time. This is actually a common complaint among players. Soccer cleats are made from synthetic leather. If you are purchasing a new pair of soccer shoes, they will be snug and stiff. Over time, there will be a noticeable stretch. This may feel uncomfortable at first, but it is not permanent.
There are a few things that can be done to slow down the stretching of soccer cleats. For one, you should make sure that you are wearing the appropriate size. If your cleats are too big, they will stretch out quickly. Another thing that you can do to slow down the stretching is to keep your soccer cleats clean and free of debris. You can do this by wiping them down after every use.