First you will need to go into Cydia and download iFile, you need to purchase the full version.
Once that's done you can now use it to unzip and move around all your files.
1st: Find something you want to download. Whether it's from your browser or an email. You will tap a download link and select to open in iFile.
2nd: You will be re-directed to iFile and you will be prompted to make a choice. On this screen, you want to select unarchiver.
3rd: It will now unzip the folder and once it's done select done at the top right corner of the screen:
4th: You are now in Var/Mobile/Documents. This is the location where all your zip/unzipped files will be placed. All themes need to be placed in Var/Stash/Themes. To do this you need to select the Edit button at the top right hand corner of the screen.
5th: Tap the theme you want to move. It will now have a check mark. You will also notice different options at the bottom of your screen. Select the clipboard at the bottom right corner.
6th: And a new pop up of options will appear. Select Cut then done.
7th: Now at the top left corner of the screen you want to hit the back button which in this location will be labeled Mobile. Each screen you go back that button will change to tell you what the next screen will be. Go back until you are in the Var folder. From here you want to select the Stash folder.
8th: Select the folder Themes. Yours may look a little different but it doesn't matter. As long as you go in to the themes folder. This is where all your stuff to use in Winterboard is stored.
9th: So in the Themes folder you want to select Edit again (top right corner) and now the clipboard (bottom right) and select the paste button in the pop up. Then done.
You are done. You can now exit the app and just go into Winterboard and select your new download and re-spring.