In WINDOWS 10
Open a console in administrator mode and go to the file folder grafana-cli.exe
cd C:\Program Files\GrafanaLabs\grafana\bin
run this command
grafana-cli admin reset-admin-password mynewpassword
C:\Program Files\GrafanaLabs\grafana\bin>grafana-cli admin reset-admin-password mynewpassword
e[32mINFOe[0m[03-20|00:08:57] Connecting to DB e[32mloggere[0m=sqlstore e[32mdbtypee[0m=sqlite3
e[32mINFOe[0m[03-20|00:08:57] Starting DB migration e[32mloggere[0m=migrator
Admin password changed successfully e[32m✔e[0m