This is the sort of tip that you think you will never need until you want to change the default association of a file, and you can’t for the life of you think what you need to do. It is very simple to do. It is aimed at beginners to the OS but many people still may not know how to do it. Its slightly hidden away.
Anyway, if you want to change the program association of a file type for example you want to make a .png open up in Photoshop instead of Preview this is what you need to do. Firstly right click on you file. Select Get Info or press Command + I. If you look down the list there should be a little flippy triangle with “Open With” this is where the magic happens. Use the drop down list to select the application you want to open the file. When you have picked you Application press Change All and it will now open every file in that application.
Optionally you can change the program association of just one file. For example if you use a file regularly and you want it to open up in a different application. Right click on a file and then press option. You should see Open With change to Always Open With. This changes the program association of that one file. Simple and effective.