Upgrade fedora 30 to 31

I am trying to upgrade from fedora 30 to fedora 31 and I ran this: sudo dnf system-upgrade download --refresh --releasever=31 --allowerasing --best After downloading about 3,000 packages, it throws out the following statements:

warning: /var/lib/dnf/system-upgrade/rpmfusion-free-updates-787aa0dc5e0e227d/packages/rpmfusion-free-appstream-data-31-1.fc31.noarch.rpm: Header V3 RSA/SHA1 Signature, key ID c481937a: NOKEY
RPM Fusion for Fedora 31 - Free - Updates                            0.0  B/s |   0  B     00:00

Curl error (37): Couldn't read a file:// file for file:///etc/pki/rpm-gpg/RPM-GPG-KEY-rpmfusion-free-fedora-31 [Couldn't open file /etc/pki/rpm-gpg/RPM-GPG-KEY-rpmfusion-free-fedora-31]
The downloaded packages were saved in cache until the next successful transaction.
You can remove cached packages by executing 'dnf clean packages'.

I am beginner to Linux and could not make sense of these problems. It would be great if someone were to help me resolve this? I am running a lenovo legion y520 with 16 GB ram. The OS is fedora scientific 30 running on kde plasma 5