This may be too easy, but Windows users will always ask...
Download and install WinSCP: https://winscp.net/eng/download.php
Connect to the Rover Wifi.
Just after you open the software it will ask you for the Rover login details, as always:
IP: 10.0.0.1 | Login: pi | Password: raspberry
and click 'login'.
Now in the right window you'll see all the files located in your Rover.
Now login to the Rover console via ssh.
and grant yourself access to modify the files. Type:
sudo chmod 777 [/upload-directory]