When you log in to a website Google Chrome will ask you if you wish to "save" the login details. This means that when you next go to the login page the email and password fields will already be full.
When you change your password, Google Chrome will prompt you to update your password to keep up to date with any changes you make.
If the updating of your password doesn't take effect or maybe you need to update your email address for the site, best thing to do is to delete the Auto-Fill and then create a new one.
First Click the menu icon in the top right corner of your browser, as circled in the image below. This will bring up the drop-down menu shown in the image below. From the menu click "Settings"
This will bring up a new page where you can edit your browser settings. Scroll to the bottom and click the link "Show advanced settings".
Scroll down to the section titled "Passwords and forms", and click the blue link "Manage passwords"
If you do not want Google Chrome to save passwords for any site, you can un-tick the box "Offer to save your web passwords"
This will bring up a popup as shown below, listing all the logins you have saved on Chrome. Click the one you wish to delete, then click the X icon as shown in the image below. This will remove that login. Hit "Done" when you're finished, and that email will no longer show up on your login page.
Once you have removed it, you will be able to re-enter your new email and password and re-save under the Auto-Fill option.
Other web browsers may have this option as well, please see your browsers help desk for information on changing this.