May I presume that by "free space" you mean your home directory...the director where you keep your files? There may be a post-install way to do this. However, when it happened to me I just reinstalled and paid strict attention to the prompts. There is an install prompt which allows you to format (don't if you have data on it) and/or just install your home directory. You have to tell it to use your home directory whether you format it or not. I don't remember the exact prompt but its there.