have adobe reader 8.3.1 windows xp sp3 reader not working right and it wont let me remove or update

I have adobe reader 8.3.1 on system windows XP SP-3. Reader not working correctly but it wont let me remove or change. I down loded Reader XI (11.0.2) but it will not open because of reader 8.3.1. How do I deactivate 8.3.1 and remove it? Reader 8.3.1 installed 9/14/2011. update ID (AC765BA86-7AD7-0000-2550-7ABC-40000831)