You first need to install OpenSSH on your phone, you can get that from Cydia. Then, if you haven't already install winterboard. Then, you need to download an OpenSSH program for your pc, The only one I can think of is WinSCP, google it to find them. Once your have access to your phone remotely go var/stash/Themes.XXX(xxx may be different) and create a new folder with the name of your theme. Then just drag and drop.