You can update the password in the following ways:
1. Adding password when creating a PageYou can add a password while creating a Page, in the 'Page Security' section. Select the 'on' button and you will be given a field where you can add a password for the page.
2. Adding / changing a Page's password
Select 'Edit Page Details' from the actions menu which can be found by hovering over the cog icon next to any Page.
Here, you will be able to add or change the password in the 'Page Security' section. Follow the same steps as you would do to add a password while creating a page (see instructions above).
The easiest way to add a password to a Page that is already created is from the Control Panel.
3. Adding password from the Control Panel
Click on the 'Pages' tab in the Control Panel.
Look for the Page you want to set the password for. You will be able to see a 'slide button' under the column 'Password Protection'
Click on this button.
A window will pop-up where you can add the password. Once that is set, simply click on the 'Enable Protection' button and the password will be saved for the page.