Here's an easy way to change file associations. Click on a document to select it, then hold the Shift key while right-clicking on it; select Open With from the context menu. In the Open With dialog, make sure there's a check mark in the "Always use this program to open this type of file" box, then double-click on an application in the Choose window. Warning: Once you've done this, the box will be checked by default next time the dialog comes up.