On my computer there are Windows and Ubuntu (the hard drive is divided). Can I delete Windows and connect it hard disk space join Ubuntu? If "yes" => how?
Sure you can. Just boot a live system (e.g. your installation medium), delete the windows partition and resize the Ubuntu partition. You can do this with GParted.
After that you might need to edit the /etc/fstab on your Ubuntu partition to set the new UUID of the resized partition - if it changes. You get all the UUIDs with
Then you can reboot and your Ubuntu should boot.