Linux is the kernel. Fedora is a distribution that uses the Linux kernel.
It is the desktop and development offshoot of Red Hat.

You have two options. You can reset the password. Or you can re-install
Fedora or any other OS that you want. You can set your own user name and
password. That may be the easier solution in the end. However, if there are
files to retrieve then you will want to reset the password. Currently you
do not know which version of Fedora. It comes out with a new release twice
a year and old releases are retired after a while. If it is an older
computer then it may have an outdated version and you may not be able add
software packages.

To Reset Password See:
fedoraproject.org/.../How_to_reset_a_root_password\
e

Basically you have to change the boot mode to single mode and then boot
from the grub bootloader (which is just a keypress - b) at which point it
will stop at a commandline where you can type the commands given to change
the password to whatever you like.

To start fresh go to distrowatch.com and download an iso image which can
either burn to a CD/DVD or use unetbootin to make a bootable usb key. You
will need another computer for that or go through the reset password on the
Dell.