All the default text and language on checkout pages are text labels and can be edited by clicking on the left sidebar (Text Labels icon) (There is no need to edit any HTML code).

It will highlight all text labels in yellow, to edit them, please click on the variable name. 

For example,  instead of clicking on "Enter Email", click on "enter_email_placeholder"

About the "Save % with this option" label: 

 The percentage can be removed by leaving this text label empty: 

Removing the whole section is possible as well: 

By leaving blank or empty these 2 text labels: save_label_billing and per_year_option_billing 

There might be some text labels that are not highlighted like the card number, expiration date and the security code. 

To edit these 3 labels, please follow the steps in the image below: 

More About Editing Sign Up Pages: