The rulesets are downloaded automatically if there's a newer one.
This mechanism stopped working recently.
Also it only worked on Linux as on Windows it's blocked by JVM keeping the .jar file open (by the class loader) - see WINDUP-702.

Key classes:
Windup/ui/addon/src/main/java/org/jboss/windup/ui/RulesetUpdateChecker.java
Windup/ui/addon/src/main/java/org/jboss/windup/ui/WindupUpdateRulesetCommand.java