There are a few ways to purge work tables (which hold temporary data for workflows or deliveries, but are commonly but erroneously called "temporary tables").
- Restart the workflow, whilst making sure the "Keep interim populations" checkbox in workflow properties is unchecked
- Stop the workflow. Then from the workflow list, select the workflow, right click it and select "Actions" > "Purge History". Be careful, as this will also delete the workflow journal/log too.
Also see documentation about database cleanup.