we do not recommend uninstalling 1.x yet, because 2.x does not support the whole API set yet. So for the next weeks until we finish the transition to Qt 5, you can keep both the old and new versions. Bug fixes and new features, however, will then only be added to the 2.x version which is why we wanted to give you access to it as soon as possible so you are able to familiarize with it.
About the install notes, it says
<h2>Download Felgo for Qt 5</h2>
Open the Online Installer and choose the <tt>Package Manager</tt> option so the <tt>Settings</tt> button is shown.
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but it’s not Online Installer, it’s the MaintenanceTool.exe in the install folder.