If you want to delete everything bbpress datawise and start again then
Dashboard>tools>forums>reset forums
Thanks!
What about users?
Anything else left to clean out?
You should be able to delete any imported users.
Deleting bbPress
If it is a test server, I guess you can always manually delete data using phpMyAdmin and start fresh.
Thanks Robkk,
Do you know which tables belongs to bbpress?
The only table I think bbPress creates is the one for importing forums/keeping extra imported forum data. Most of the data bbPress has are stored in WordPress tables, but all that data should be gone if you ran the reset forums tools(well except the forum roles).
Stored Database Data
If you are looking to delete users you can go into Users > All Users in the WordPress backend and then start bulk deleting users.