Is it possible to upgrade windows 8 to 8.1 by Downloading the Updates Only?

I currently have a windows 8 pc and i would like to upgrade it to win 8.1.I would like to know if i can get it done by downloading and installing the 8.1 updates only or only by installing a fresh copy of win 8.1.

PS:The upgrade option isn't visible in the WIndows 8 Store