Dear Harish, IIT Delhi has scheduled diiferent correction windows for different correction categories. The tentative dates to make corrections to your Category would be from the last week of October to 1st week of November. This is tentative and so please keep an eye on the official website. You can change your Category but you will not be refunded any additional amount that you paid towards your application form. For more information, please visit our page at: https://engineering.careers360.com/articles/gate-application-form-correction