I will shortly be changing my ISP does anyone know how I inform Facebook of this and will I still be able to keep my friends presently listed on there?
Facebook isn't connected to your ISP, so will run as it always does. if you change your email addy you should change it in your settings and on your profile, if it's visible.
It'll have absolutely no impact on your facebook account. Except that if you don't use that email address, then you won't receive notifications, unless you change your email in your FB settings.