This article will show you how to change your password. If you suspect that your account has been compromised, you can change your password and logout of all devices with an active session.
From your account, click on your name on the top right corner and select My settings. Then select Choose a new password.
Change your password
Enter your old password and your new password in the corresponding fields. Tick on the box Sign me out in all other devices in case you suspect your credentials have been compromised.
Read the tips on how to choose a good password.