This question already has an answer here:
I was trying to install some plugins for my navigational program when I noticed I can't do changes to the file. And after a while I noticed that I'm not allowed to do any changes to the filesystem.
The properties-permissions window for the filesystem tells me:
You are not the owner, so you can't change these permissions.
How did that happend? How can't I own my computer (only account on this laptop).