For your security you must change the password immediately when you enter the back-end of your website.

To change the password of the site, you must have entered the administration panel.

At the top right, click on the user menu and then on "Edit account"

The previous action will take you to a page with all the information of your account which can be edited and in the "Password" box, you must enter your new password and repeat it in the "Confirm Password" box.

It has several other options that you can configure, at the end you must press "Save"

The password was changed.