Photoshop not recognised as default app after OS update
Go to the file in Finder. Right click, and select 'Get Info'. This will open up a new window with all the file information. There are different sections in this window. Scroll down (or collapse the sections) until you get to the one titled 'Open with'.

There should be a drop down select menu that shows which program will be used to open the file. The default program will say "(default)" after the program name. Use this menu to select Photoshop. If it's not one of the options in this list, click 'other' to select it manually. If these are Photoshop files, OS X should recognize that Photoshop can open them, but if it is greyed out, select "All Applications" from the "Enable:" drop down menu.

Back in the file info window, below the program select drop down, it says "Use this application to open all files like this one." Click the button that says "Change All" (directly beneath this text) to make the selected program the default.

If any part of this doesn't work, my guess would be there is an issue with the Photoshop installation. Check that you can still use the application with other files. Reinstall the application and try this again.