do we need to uninstall outsystems 9.0.0.36, if we need to upgrade from 9.0.0.36 to 9.0.1?
You can just upgrade to the new version.
Here you can find the checklist:
http://www.outsystems.com/home/document-download/1182/88/0/0 (.NET)
http://www.outsystems.com/home/downloadsdetail/88/1183/ (JAVA)
The first dropdown states the kind of task. First install or upgrade.