We know that we have made decisions in the past. Looking back on them, we cannot change having made those decisions, yet we know that we have made them, that we have engaged in a thinking process which led to a decision being made. Does the fact that we cannot change the decisions we have made mean that we do not have free will?
No, of course it doesn't.
Now, flip that, and apply it to the future. If you have prior knowledge of a decision you will make, then most likely that prior knowledge will be part of that decision, and you will make it. Does that mean the decision is inevitable? Maybe. Does that mean it wasn't a decision? No. You simply know what you will use your free will to decide.
This situation is also only problematic given a linear definition of time. If time is not linear, 2 dimensional, but in fact non-linear and 3 (or more) dimensional, then we must figure that in a sense all of time is simultaneous and the problem of free will is only a problem from a certain, limited point of view.
Alan Watts gave an example of a snake in regard to time and causality. The illustration probably predates him. Anyway, if you can only view the world through a small, stationary slit, and you see a snake pass by, first you see the tip of its head, then its head, sliver by sliver, and its body, and finally its tail. If it turns around and crosses again, you see the same thing, only by the other direction.
With this limited view, you may come to think that the head predates and causes the body and tail, and the body and tail are necessary consequences of the head. But, this is nonsense, because we know the head no more causes the tail than the tail causes the head. The snake is a complete, simultaneous entity.
If we view time and causation in this way, we may see it from another perspective, that time, perhaps is actually 3 dimensional and that the past causes the present and future no more than the future causes the present and past. But, rather, time is like a snake existing all at once, and it is only our perspective that makes it appear linear.
That being said, I think neuroscience is going to trump philosophy and religion with regard this and many other questions we have about the nature of free will, consciousness, and other issues.