It's on the journey check pages found by clicking on 'Live Train Information', in the General Updates box.
Not quite as intuitive as could be.
Paul
Indeed - it appears under "General Updates", entitled "Important Changes to our Monday to Friday Timetable". As just two trains are involved, and will be cancelled, it would be easier to find under "Other Train Service Updates" - where similar items do appear - or even "Train Cancellations", and identifying the trains involved.
The downloadable posters, as well as the printed ones, still show the train. There is no correction on the selector page for the timetables, though another short-term change (Raynes Park-Waterloo trains skipping Clapham Junction) is there.
Today I found this poster at Wokingham, inside the station, but none at Reading (the odd angle is to minimise reflections). Of course the change starts next Monday, so regular travellers needed to be told by tonight at the latest. I hope there was more warning at Virginia Water, as the train running just ahead of this one (uniquely) doesn't call there and the following ones are slower.