How to set/change a checkbox checked atribute in html code

I have an input page where users enters the attending hours for a business, it displays each day schedule and the user can enter the open and close time, also have a little checkbox saying it is 24 hours open, if the business wil be open 24 hours the whole week, i want to avoid the user from clicking 7 checkboxes(one for each day) instead, i have a radio button which says "24 hours" and i want that when a user clicks on it it will check the 24 hour checkbox for all the 7 days automaticaly. i just don't know how to check/uncheck a checkbox once it has been created or displayed