What is required to upgrade a laptop hard drive?

I’ve got all the files I need migrated to an external. What do I have to do to migrate windows to the new hard drive? What do I need to look for when shopping for a new hard drive? Specifically I’m working with a dell inspiron e1505/6400 laptop. Physically, removing and replacing the hard drive isn’t a problem I’m just having trouble finding what to do about operating system and programs. Anyone?