How to delete charts and dashboards？
If I am not wrong, you always need to archive things you want to delete, then go to <metabase_url>/archive and delete things you do not want anymore.
To archive dashboard, edit them and then click on “archive” (between “save” and “cancel” button)
To archive question, edit them and then click on the “archive” icon.
I am using the last version (v0.32.2) so I do not know if it is the same for previous ones.
Hope it helps !