David can you please list exact cart version in your signature - 4.4.x? You get better help as versions are different.
The phone numbers you are asking for are in admin/settings/company - just login there and change them to whatever you want.
Changing the skin will not undo whatever you modified but it may not load it if you modify it for a specific skin.
You don't upload images yourself - if you use the admin interface to assign images to products, categories, manufacturers XC uploades them in their appropriate directories, if you use CVS file to upload info you can upload images to new directory on the server and specify on the upload screen - XC will copy them accordingly.
Just so you know -
http://forum.x-cart.com/showpost.php?p=250406&postcount=4 - there are few more directories in there but these are the main places