There's a few guides if you search - they worked for me - but I found mine difficult to remove even with them. I popped the two clips/tab inside the top of the vents with thin screwdrivers, and managed to get my fingernails under the edge of one side to pull it forward enough to keep the clip/tab disengaged. I then worked the same on the other side but it wasn't easy!
I carefully pulled on the adjusting tabs too, but I was worried about damanging them as well.