Hello @rparr009,
KNIME software and KNIME workspace(s) are usually on different locations so with uninstalling previous KNIME version and installing new one you shouldn’t lose your workflows and respectively your data. Upon first start up of new version simply your existing workspace as default. However it is always good to do regular backup of your workspace. You can do this by doing simple copy paste on OS level or as @Coral_OBrien said, by exporting your workspace.
To retrieve list of all installed extensions see this topic:
Welcome to KNIME Community @Coral_OBrien!
Br,
Ivan