Replace Windows+Ubuntu(installed with Wubi) with Ubuntu 14.04

I currently have Windows 8 installed on my machine. I installed Ubuntu 12.04 a couple of years ago using Wubi and eventually just started using Ubuntu. A couple of weeks ago, I learned that Windows on my machine was corrupt and needed a reinstall. Ubuntu works fine, but is kinda slow and clunky. What I'm wondering is that if I install Ubuntu 14.04 as per the instructions here and choose the replace Windows with Ubuntu option, will it also delete the Ubuntu 12.04 installation? Or will I have to delete that manually? All my important files are backed up on Dropbox so I don't really care about those.