Take off the rubber mouldings... then remove the entire top trim/bracket with a phillips head screwdriver (total of 6 screws I think)
Turn it around and you will see a few clips holding the weather guard onto the bracket. Remove these carefully so you don't bend the aluminum bracket. Re-mount as required.
To clean the stuff off the actual rubber without using a blade that can damage the trim, I used a substance called Prepsol which is like an alcohol.
What it does is "freeze" the tacky stuff so you can either scrape it off with a credit card or your finger nails. Took me a good few hours to get it clean, but I got there