How can wingtip vortices affect the direction of the relative wind in front of the leading edge? I have a question on aeroalia's answer on this post (Why does the vortex created by wing affects its own angle of attack?). 

If I'm not mistaken, wingtip vortices are generated behind the trailing edges of the wings and, even if we assume wingtip vortices somehow can reach the front area of the wings, it would only be able to affect the relative wind in front of the leading edge on the far outboard of the wings close to the wingtips, because after all it's wingtip vortices. Then, how could it be said that the upwash from the wingtip vortices changes the direction of the entire relative wind?
Please don't believe everything you read. You healthy scepticism is your best defense against the nonsense you might read about wingtip vortices.

What causes the flow to increase its angle when approaching the leading edge is the low pressure region above the wing. This is not only the main contributor to the wing's lift, but also the reason for the flow pattern ahead of the wing, in combination with the overpressure region around the stagnation point.

Please read this answer and let me know if something is left unclear.