Cant install over Vista

I want to do a clean install over Vista but it gets to the point where it asks what to save and i put nothing but it wont go past it. It leaves a message that i need free up disk space.

Perhaps you need to use this tutorial: Clean Install - Windows 8. You should never get to where you are. Unless, per chance, if you are using the windows 8 upgrade assistant approach. If so, then use this tutorial: Windows 8 Upgrade Assistant - Download and Run. Choose the option of downloading an ISO--that you can use to create an install disc or USB flash drive and, then, do your clean install.

Hello Pokalong, and welcome to Eight Forums.

Since you want to do a clean install instead of an upgrade install, you might consider downloading the Windows 8 ISO file using your purchased product key instead. Afterwards, create a bootable Windows 8 installation DVD/USB with the ISO.
This way, you could then do a clean install with your upgrade copy of Windows 8.

Hope this helps,
Shawn