Нашёл ответ здесь
http://www.youtube.com/watch?v=U51k118-bFg
сделал примерно так
monday=(ImageView)findViewById(MONDAY);
tuesday=(ImageView)findViewById(TUESDAY);
wednesday=(ImageView)findViewById(WEDNESDAY);
thurday=(ImageView)findViewById(THURDAY);
friday=(ImageView)findViewById(FRIDAY);
saturday=(ImageView)findViewById(SATURDAY);
sunday=(ImageView)findViewById(SUNDAY);
layoutMonday = (LinearLayout.LayoutParams)monday.getLayoutParams();
layoutTuesday = (LinearLayout.LayoutParams)tuesday.getLayoutParams();
layoutWednesday = (LinearLayout.LayoutParams)wednesday.getLayoutParams();
layoutThurday = (LinearLayout.LayoutParams)thurday.getLayoutParams();
layoutFriday = (LinearLayout.LayoutParams)friday.getLayoutParams();
layoutSaturday = (LinearLayout.LayoutParams)saturday.getLayoutParams();
layoutSunday = (LinearLayout.LayoutParams)sunday.getLayoutParams();
bigWidth=layoutThurday.width;
bigHeight=layoutThurday.height;
smallHeight=layoutMonday.height;
smallWidth=layoutMonday.width;
Изменение размера при нажатии клавиши:
....
layoutMonday.width=smallWidth;
layoutMonday.height=smallHeight;
....
layoutThurday.width=bigWidth;
layoutThurday.height=bigHeight;