Firstly, sign in to the Storefront Admin area as normal
Once signed in to your Admin account to change your password click the "Person" icon top right.
1. Manage Account
Click the "Person" icon to open the Account submenu, select "Manage Account"
1. Confirm Password
Enter your current password again to edit your Admin Account, and click the "Confirm Password" button
Enter your new password
2. Confirm password
Retype your new password
Click the "Save" button, to save your new password
Your Admin Account is now updated, you can continue to use the Admin and next time you sign in to Admin you need to use your new password next time.