How do I mark a checkbox up to the selected value with dropdown?

Without knowing anything about those checkboxes, like how you identify them on the page, it is impossible to give specific advice. Make the "value" of your select options the number of checkboxes you want to "mark";

<option value="10">1-10</option>

read that value in javscript, get a reference to all of the checkboxes then in a for loop set them to be checked.