According to this sitethis site, the default root password is "toor" https://forum.porteus.org/viewtopic.php?f=81&t=1062toor.
If you can log in as root using that password, you should be able to access that folder. If you are logged in as a guest, then from the command line you can switch to root with the command "su root"
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 dolphindolphin should give you access through a GUI file manager.