If you access problems, try the following things:
Type in "su", without the quotation marks, to go into super user mode. That will give you full permission to update the system.
If that doesn't work, you may need to change the permissions of the files themselves. To do that, you use the chmod command.
In the prompt type in:
chmod 700 file.name
That would make the file, readable/writeable/executable to the owner (first number), but neither to user and group, which applies to other users that login. if you want them to be able to read the file, you would change 700, to 755, which is read an execute.
check here for more info).
HTH