How to delete sample data?
The quickest way is to:


Run a contribution search with no criteria. You will have a result page with all of them.
For the Select Records option, choose All Records.
For the Actions option, choose Delete Contributions.
Repeat for contacts with Advanced Search; type "Sample Data" into the "Contact Source" field to find all sample contacts and then bulk delete them. This will cascade down to delete events, activities, etc. You'll also get a message that your own record can't be deleted, so there's no concern about wiping yourself out of the system.