If you have previously recommended this thread, you should see a tick / check mark on the recommend button. Click the tick to undo the recommendation (the tick may appear to change to a cross as you do this.) If you added a comment with your recommendation, you will need to delete that from your facebook wall separately.
There are two seasons. One is in the summer, after exams, and the other is early autumn. Get on to the website of your target Universities and find their specific dates. The very popular ones get filled up quickly so make a note in your diary of the date they open online booking.