Open the Simatic Manger, if it is already opened close all the other editors, VATs, Symbol tables etc.
If you've already got your project opened in Simatic Manager, When you click on File > Archive, it will already be highlighted in the project list, if not just choose the file you want out of the list of projects. Then Click on OK and choose the destination and file name (if you don't like the one offered by Simatic Manager) in the next window before clicking on Save (or is it Store - I've got the German version so I'm not sure.
Your project will then be stored as a .zip file with all the project related info included.
To recover a backup use Menu > Dearchive (? recover/restore?). Note that when you want to restore your backup you'll be asked if you want to overwrite the existing directory, before you click yes make sure the project is not open in Simatic Manager, otherwise you'll get a message saying that SM was unable to delete the directory.
If you're going to be making regular back-ups which is sensible on a new projects, don't just overwrite the old back-up, but use Explorer to rename the old file first. If you rename to yyyy_mm_dd.zip, you'll be able to see at a glance which versions you have available. If you have a major crash or go off at a tangent which turns out to be all wrong, then you can easily get back to a defined starting point.
If the 313C is the last version you won't be able to extract hardware configuration, but the program. If you want to upload the hardware configuration you will need STEP 7 5.2 and some SP.