Step 1: Uploading the Save
1. Navigate to C:\Users<YourUsername>\Zomboid\Saves\Multiplayer
2. You should see your save folders in here. Find the one you want to upload and make a copy. Rename this copy to pzserver
3. On your server, open the file manager tab and login. Navigate to /server-data/saves/multiplayer/
4. Download, delete, or rename the existing pzserver folder. This is your previous save on the server so you can do what you want with it. It just can't be named pzserver in this folder.
5. Upload your pzserver folder you renamed on your PC and upload it to /server-data/saves/multiplayer. It is best to do this in a zip file and then right click and extract.
6. Restart your server. You have now moved your save to your server.
Step 2: Transferring Characters
1. Assuming that you've uploaded your save folder, you will just need to change a file in your pzserver folder on your server.
2. Open /server-data/saves/multiplayer/pzserver/
3. Press control+f to find the file called "players.db"
4. Download players.db to your PC.
5. Use a program such as https://sqlitebrowser.org/ and open the file in it.
6. When in sqlite, click the "Browse Data" tab.
7. Where it says "Table:" click the dropdown and select "networkPlayers"
8. There is a world column. Change all of these values to "pzserver"
9. Save your changes and upload it back to pzserver on the server, replacing the old one.
10. Restart your server and your characters will have transferred.
Step 3: Making the Admin Account Work
1. Once you've done your characters and save, you may notice that the built in admin account no longer works. This is an easy fix.
2. Navigate to /server-data/db and delete pzserver.db
3. Restart the server and the account will work. Keep in mind this will reset all permissions and the only admin will be the admin account until you give other players permissions using that account.