Tool for File Recover | Deleted Files Recovery
The problem with deleted files is that they no longer have inodes and a lot of the data about the filename and how they're linked together is lost. It's not like in windows where the filesystem just renames the file.
There are ways to do it, you can follow some of the guides here:
http://e2undel.sourceforge.net/recovery-howto.html
They show you some of the tools which use heuristics and guessing to put data back together.
The first thing to try is the Trash bin.
Go to Places -> Home Folder
Then click on Trash
If the file is there right click and then select Restore.
If this does not help try following the official ubuntu data recovery instructions here
https://help.ubuntu.com/community/DataRecovery