Step 1: Go to "login.microsoftonline.com"
Step 2: Sign-in with your Office 365 Email and Password
Step 3: Go to the Apps Tab and select "Admin"
Step 4: Go to "Users" and select the user you wish to modify
Step 5: Select "Reset Password"
Step 6: Choose whether to Auto-generate or Create your own password
Step 7: Shown is the new password for that email. You can also select whether or not to send a email to yourself with the new password