If you need to change your office 365 password this can be done easily from your Office 365 Homepage.
On the Homepage click on the settings icon (the ‘cog wheel’, top right of the screen next to your picture or initials) and under “Password” choose “Change your password” from the options that show
On the next screen simply type in your new password, then type it a second time to confirm it and click on ‘Submit’
Your password should contain at least one capital letter and a number, and it will be stronger if you add a “special character” (e.g.: ! _* & and so on)