I no longer have iLife.app in my Applications folder I no longer have iLife.app in my application's folder. The latest version of iLife I have is iLife 11 from Snow Leopard: OS X 10.8.6, which resides on my MacPro 1,1.

I purchased my new iMac (2013 27″) new from B&amp;H, in SEPT 2014, Serial Number: D25N116JF8JC; it came with the Mavericks operating system. However, in late 2014 I upgraded it to Yosemite online. I didn't like it because Yosemite no longer had colored folders and text instead it only had colored dots, so I took my iMac to an Apple Store in King-of-Prussia, Pennsylvania had them return my operating system back to Mavericks.

I must have lost iLife at this time. 

I have now upgraded my operating system back to Yosemite. But, I have lost my iLife app altogether. So I cannot upgrade iDVD which is now 7.0.3, and now I get an error message saying I cannot upgrade iDVD to the next level. Also my iMovie HD.app is 6.0.3. Can you help me?
iLife 11 was sold on physical media, find the iLife box or the restore media that contained it, and you should be able to reinstall from that.

Or a trip to the Genius Bar should get that resolved too.