Send unused docs to trash
Click on the three dot menu to the right of your channel or doc (in the sidebar) to send it to trash:
Restore or permanently delete docs
When you send your docs to trash, you still have a second chance to either restore it or delete it permanently. In a way, the trash bin is also an archive, since it won't be cleared automatically.
Just head to the Trash on the bottom left of your admin, and click on your docs' three dots to view the options.
Who can delete docs?
Permissions for channels apply to all docs within them, even deleted docs.
Private docs remain private (restricted to the person or people who had access originally), even after being trashed.
"Reader" permissions in a channel won't allow a member of your team to send a doc from that channel to trash, or to permanently delete it.
"Writer" permissions in a channel will let a member of your team send docs to trash, but not delete them permanently unless they are the doc's author.
"Admin" permissions in a channel will let a member of your team send a doc to trash and permanently delete it.