How do i clean my laptop so i can sell it without having my identity stolen?

thanks. i wanna sell my laptop so i can buy a new and better one but dont want all my information that i have on it stolen or used in some other nepharious way. can someone instruct me in detail as to how to wipe it clean without losing all my office software? is that even possible? i guess if i have to lose the software fine, but id prefer to keep it on there bc it will add resale value; thanks.