You can quickly and easily change the application that is used to open a specific file. Simply click on the file fro the Finder and then select Get Info from the File menu (or click on the file and then use the Command-I keystroke). Once there, click on the Open with: disclosure triangle to see the application that is currently being used to open the file. You can click on the arrows to select a new application for that file.
You can also use this same screen to change the application used to open all files of a type. To do so, click on Change All…
