Please see https://releases.xamarin.com/service-release-15-5-3/ for the details about this release, including the steps to update.
This release is now available as part of Visual Studio 2017 version 15.5.3 and in the Stable updater channels for Visual Studio 2017 for Mac and Visual Studio 2015 Tools for Xamarin.
Please report a bug if you see any new issue with these versions or any errors in the release notes.
Comment in this forum thread if you get any errors when submitting an issue. Thanks!