Well, that depends on what database you are using. If you aren’t using anything special (I.E. the basic database), then just delete the file. You could also attempt to use the purge database service. Not sure if it exists for the basic database though.
Purged the db, i assume you mean home-assistant_v2.db? if so thats what i deleted, here is my config.yaml, still showing ecobee in celsius
homeassistant:
# Name of the location where Home Assistant is running
name: Home
# Location required to calculate the time the sun rises and sets
latitude: 38.5816
longitude: -121
# Impacts weather/sunrise data (altitude above sea level in meters)
elevation: 0
# metric for Metric, imperial for Imperial
unit_system: metric
# Pick yours from here: http://en.wikipedia.org/wiki/List_of_tz_database_time_zones
time_zone: PST
# Customization file
customize: !include customize.yaml