i have the link for upgrading my zen cart... but (call me stupid) im a little confused...

1. i dont know how to upload my 1.3.8 version (with all add ons etc) to my pc to compare and change 1.3.9 so if i dont do the comparision will it delete the add ons or text i put in since i installed it 2 years ago?

2. do i make a new folder in my cpanel files as "new store" and upload it there.. if so. how will my cpanel KNOW to upgrade and run the new version?

i need to most "stupid proof" explanaition if anyone can help....

please and thank you...