Step 1: Login into portal.office365.com
Sign in with your Login ID and Password.
Step 2: When entering account click on Admin as shown into the picture.
Step 3: In Admin panel click on the Security Tab and expand it.
Step 4: Now again click on the Setting which is shown after expanding the Setting Menu.
Step 5: In new window click on Security & Privacy.
Step 6: Now click on the Password Expiration Policy and If the password is set to expire, you can change the password age or the length of notification and click on Save Changes.