I can´t save files from the browsers anywhere + other questions

Hello there peeps!

Im having issues with my Macbook Pro Retina, running latest Yosemite (late 2013 model). This is my first Mac so I feel kinda newbish to OsX since I´m used to Windows.

I think it began when when I changed my user name. At first I could only save files from the browsers in the users home and directories created by myself in the "root" of the home dir. NOT in the default directories like Downloads and such.

I searched for help and tried the built-in Disc Utility and I downloaded Maintenance and tried them.

It didn´t help and now the problem is worse, the browsers say there is not enough disk space even tho Ive got over 50gb left.

What to do? This problem only seems to be with the browsers.

I also wonder if its safe to delete all the built-in apps I never use like Itunes, Photo booth, Ibooks, Game Center, Chess, Mail?

What version of OS X are you running?

Changing your user name probably messed up your file/folder permissions. If you open Finder -> right click on a folder - say your documents folder - and scroll down to Get Info -> Sharing & Permissions, you will see a box with Name and Privilege. Under it will be the users in the system and what privileges they have to that folder. You can change them and for your user name it needs to show Read & Write.

Lisa