As you learned earlier, you can right-click a file and choose an application to open it with. However, you may want to make a permanent change. For instance, perhaps you'd give anything if you could just make those JPGs open in Preview again. You can -- and here’s how to do it on just about any Mac imaginable:
1. Open Finder and locate any file that’s opening in the wrong program. This might be an RTF file that opens in TextEdit instead of Word, or a JPG that opens in Photoshop instead of Preview. Select the file by clicking once, but do not open the file itself.
2. Choose File>Get Info, or if you’ve added that command to your Finder window as detailed in the previous section, click the Get Info icon. (You can also right-click the file.)
3. In the Info dialog box, expand Open With by clicking the triangle, and from the Open With choice, select the new program you want this particular file to open with. (We'll stick with our m4a file here.)
4. If you want all other files of this type to open with this same program, click Change All. Verify your choice by selecting Continue in the resulting dialog box.
5. Close the information dialog box.
click to enlarge