Hi @thesun2012,
Thank you for using Paid Memberships Pro.
We do not have a way to bulk delete orders from your WordPress website back-end & when you delete users, their orders are not deleted to prevent the inconsistency with your PMPro reports. The alternative no-code way to do this would be to delete these others individually from your orders
page.
While it is possible to bulk delete your orders, this can be done via custom code and requires having the technical expertise required to do so. Please see this bit of code you or your Developer may modify to work with: https://gist.github.com/strangerstudios/8621990#file-pmpro_clear_all_data_init-php
If you need technical help, please contact a local WordPress developer on https://jobs.WordPress.net for further assistance.