Purge Old Entities (After MQTT Migration)

Rightly or wrongly after migrating from ZHA to Z2M I now have a bunch of old entities that no longer exist.
Similarly while playing with templates I created a bunch of templates, but they still exist even though I removed them from the yaml file.

Is there a way to purge these from my system?

Is it just 1 at a time to purge or is there another way?

In the Settings → Devices & Services menu → Entities list you can select multiple entities for deletion.