According to this site, the default root password is "toor" https://forum.porteus.org/viewtopic.php?f=81&t=1062
If you can log in as root using that password, you should be able to access that folder. If are logged in as guest, then from the command line you can switch to root with the command "su root", and then enter root's password. As root, you should be able to access the folder you are trying to access. Additionally, running a file manager like dolphin should give you access through a GUI file manager.