I want to install Ubuntu on my laptop and I want to let it use all the hard drive so it could delete my former OS but i have a large file on my C drive witch is the only drive and I am wondering would the file stay or will it be deleted when i ask the wizard to use all of the hard drive. Sorry if its a stupid question.
Yes, it will.
- pick "replace windows" at the installer and -anything- related to Windows will get deleted.
If you need a partition that remains as is use a tool in Windows (gparted) to shrink a partition and pick the "something else" option in the installer and then use the unallocated space to install Ubuntu.
But... you start with making a backup.
Yes, it will be deleted. If you intend on erasing Windows when installing Ubuntu, use a flash drive, SD card, Google Drive, Dropbox, etc. to make backups of all your important files.