The suggestion to backup files is precautionary...we cannot always expect things to go as we anticipate.
What reference are you using for this anticipated upgrade?
You can use a program like Macrium Reflect FREE Edition - Information and download - http://www.macrium.com/reflectfree.aspx
to do the backup.
You need to be aware that your access to files that are backed up...will include everthing...but you will be able to move data files only. None of your programs are moveable, they must be resinstalled...if you are doing a clean install.
What method are you using to do the upgrade?
System manufacturer and model?