working with an off line copy

hi group

i want to work on websites “off-line” to check them out properly before uploading.
i am using wamp, i think i know how to export the site to upload and get it going but what happens then..

if i upload a site and keep working “off-line” can i then synchronise the two?
or do i have to upload the whole site again?
and if i have to upload again do i have to delete the old “on-line” site?
and if i do have to dlete the “on-line” site will my rankings get effected in deleteing and re- uploading?

i look forward to your replies.