If you are still able to log in to the account, you can change your password in your profile settings. More information can be found here: User Profile Settings
In case you can't log in anymore and you want to reset your password, you should be able to find the “Lost Your Password?” link on the login page.
Click on it and enter your email address - The email will be sent to your inbox.
You need to open it and change the password within 20 minutes as it expires afterwards.
If you are not able to reset the password, check the following article for troubleshooting here