It is a bit hard to do it from GuidedTrack directly, it will probably be a better experience if you do in processing step with your analytical software (spreadsheets, R, etc).
To exclude records from test runs or bad you can mark these rows in your Data tab as Preview like this:
It is not possible to remove unnecessary columns, unfortunately. In order to ensure that no data will be lost all changes in questions are saved as separate columns. It might be useful for future runs to copy the code to a new program — it will then have only necessary columns as there will be no question history for the new program.