The system generates a debug log for a user every time that user executes a transaction and the user has a trace flag with start and expiration dates that contain the transaction's start time.
When you add user to trace for debug, you have to select an existing Debug Level or create a new Debug Level.
To add new Debug Level, click New button in Debug Level lookup window.
You can modify existing debug level by click Debug Level name, then adjust debug level for each Category.
However, over the time, you may get more and more debug levels added and may you decide to delete old levels no longer needed. Here is the steps:
1. Open Developer Console
2. Click Debug | Change Log Levels...
3. Click Add/Change under any DebugLevel Action
4. Select Debug Level you want to delete | click Remove button
5. You also can edit debug level for each Debug level