How to upgrade Bitcoin Core from 0.18 to 0.20 on Ubuntu 18.04?
This is how I usually do it. Check the wget links in https://bitcoincore.org/bin

# Download Bitcoin Core packages for Ubuntu

wget https://bitcoincore.org/bin/bitcoin-core-0.20.0/bitcoin-0.20.0-x86_64-linux-gnu.tar.gz

# check the checksum and fingerprint //optional
wget https://bitcoincore.org/bin/bitcoin-core-0.20.0/SHA256SUMS.asc
wget https://bitcoin.org/laanwj-releases.asc
sha256sum --check SHA256SUMS.asc --ignore-missing
    &gt;expected: xxx.tar.gz: OK
gpg --import ./laanwj-releases.asc
gpg --refresh-keys
gpg --verify SHA256SUMS.asc
    &gt;expected: Good signature from "Wladimir J. van der Laan ..."

# extract, install and check versions of the binaries
tar -xvf bitcoin-0.20.0-x86_64-linux-gnu.tar.gz
sudo install -m 0755 -o root -t /usr/local/bin bitcoin-0.20.0/bin/*
bitcoind --version
    &gt;expected: Bitcoin Core version x0.20.0