Oh gosh... I'm sooo sorry!
First off, you need to know that you are not the only one! It happens to all of us. When this happens to me, I tell myself that learning is NOT free.
This upgrading feature should be disabled. I had a lot of problems with it too.
First off, you need to know how many partitions you already have on your computer. I guess you only have one hard drive right?
Go to your terminal and type : sudo fdisk -l
Please post here all your partitions that you have on your hard drive such as /dev/sda1, 2, 3 etc.. with the type 83, I guess you only have one partition?
You might be able to recover 'some' files... Most probably not all of them because you ended up reinstalling ubuntu probably on the same partition.
Try photorec application. Here it is: http://www.cgsecurity.org/wiki/TestDisk_Download
Another good one is http://www.r-tt.com/free_linux_recovery/Download.shtml
Remember that you will probably end up recovering your files bit by bit so there will be corruption in some while others will simply not be recoverable.
I know it's very frustrating. It happened to all of us. I guess that's the way we learn.
Always make a backup!
Go to your ubuntu software center and type 'backup'. Install a backup software and start using it.
All of us have too much stuff to back up so we postpone to backup. My best suggestion is that you need to group what is important and what is not in your documents. Start by only backing up what is important to you... On a daily basis (or at the very least weekly). Keep a backup off site also. That way, if you get stolen, you will still have your offsite backup you'll be able to recover from.
Trust me, this happened to me too.