I've decided to add some screenshots to help out since I understand that looks for the Download app can be confusing.
Below is a screenshot of my home screen and what I need to click to get to all of my apps. There should be something similar on whatever phone/tablet you are using.
http://i50.tinypic.com/t6v0wj.jpg
This is a screenshot of the app that you are looking for:
http://i48.tinypic.com/1zn0ai9.jpg
When you open up the Downloads app you should see Facebook (build 140579). On my phone I had to hold down on it and drag it to a trash can. Once I removed this it took care of the issue.