You delete all specialisations of workflowusertask and workflow, and then resolve the resulting errors. Thats more or less it. If you want to distinguish between them you can give each usertask type a specific name
Beware that Workflow also had a major change from 9.10 to 9.12. Consider upgrading to 9.12 if you have the chance.
Take a look at the mendix documentation for migrating mendix workflow to 9.10
Hope it helps!!!