- From the Dev Console, choose Debug->Change Logging Levels...
- Under "Class and Trigger overrides" click the Add Button
- In the dialog, select the desired class
- Set logging level
However, step 3 is broken. The dialog includes a type-able picklist, but it is only showing me trigger names. If I just type in a class name and click the Add button, an override record is added to the table with a blank name. If I type in a class name that overlaps a trigger name (for example, I want to set logging for "dlrs.RollupService" but there's a trigger named "dlrs.RollupServiceTest2Trigger"), any attempt to click "Add" causes it to autocomplete the trigger name.