Alternatively, if you are able to access grub/grub2 entries then you can reset the root password by booting into single-user mode (runlevel 1). That is, append "1" at then end of the kernel line. After Fedora boots, just use the passwd as suggested jpollard.
p.s. This shows how important to protect the grub entries with password. But then again, if some stranger can access your machine physically then all bets are lost. I hope you are not playing the "stranger" role here