I'm guessing too here as you were not too specific.
What I am guessing is that you are OUT OF SPACE to allow you to bring down and install the Windows 8.1 update? Is this correct? I think that one was large?
You are then asking how to make space on the hard drive to do this and then RESTORE the deleted items?
Well, the real answer is it will be hard to do. It can be done, but you have to be 'selective' and items you want to delete you have to have the capability to restore after the update. Assuming you do NOT have another hard drive you are probably relegated to R/W DVD drives (unless double layer or BluRay capability on the computer and media to match) you'll be looking at 4.7GB's or so max. per DVD. What you copy off should be 'stand-alone' too. Get enough DVD's to handle the amount of space you need.
Normal back-up programs do usually require another hard drive to put the back ups on though.
Another ''risky' alternative would be to turn of the Shadow copy (AKA System Restore). That can take up to 15% of your disk drive size. You'll lose all your System Restores, but you might be able to install the update and then put back on System Restore.
If you question was for something else, please post back with more details.