Once you install the OS, you can use the Mac App Store to update to any of the later versions of OS X, as well as purchase and install many apps for OS X.
Let's take the upgrade or downgrade question as two separate inquiries.
Can I upgrade or downgrade to Snow Leopard (OS X 10.6)?
However, if IU Secure is your only option, see In Mac OS X, how do I connect to an IU wireless network if I am booted from my Recovery HD?
Hold Cmd-Shift-Option immediately after you double-click the application icon.
See this video for a walkthrough on resetting Photoshop's preferences: How to Reset Photoshop Preferences File For additional instructions, search your product's Help system for “restore preferences.” Some Adobe applications are designed to run only on an OS that has the language configured to match the language of the Adobe product.
If your computer does not support Yosemite or you would rather have Lion, you may still be able to purchase it directly from Apple (1-800-MY-APPLE).
To reinstall or recover Lion, you must have an active Internet connection.