After the line starting with 'If you're using a particular branch ...', the text provides the command
git pull
At least for MSysGit (Windows portable Git version) picking up the latest changes after switching to a particular release branch, it needs to be
git pull https://gerrit.wikimedia.org/r/p/mediawiki/core.git REL<release number>
After updating the repository, especially after switching to a particular release branch, I have to clean the local repository:
git clean -df -e extensions -f -q -x
I have no linux to compare with, therefore I did not add this to the article.