I rarely update the hugo binary I use, but when I do this is how:
First. go to https://github.com/gohugoio/hugo/releases and find the latest version number. It’s important to copy it correctly, as the URLs are constructed from it. 
pushd /tmp/ > /dev/null && \
curl -LO https://github.com/gohugoio/hugo/releases/download/v=hugo_version=/hugo_=hugo_version=_Linux-64bit.tar.gz && \
tar -xzf hugo_=hugo_version=_Linux-64bit.tar.gz && \
chmod +x hugo && \
mv hugo -f =install_path= && \
popd > /dev/null && \
which hugo && \
hugo version
That’s my default install path, but I added it as a field in case I need to install in a non-standard location but feel super lazy otherwise… 