Run this in terminal:
That will make you the owner of the file and allow you to modify it's contents without admin privileges. And no, there is no folder where you have to store source code. Any place will do. I store mine in /usr/local/src/. It really doesn't matter. Not that it's always a good practice to have on folder where you keep all the code, just for simplicity's sake.
sudo chown username:username /usr/src
EDIT: As noted by Teo, you can extract to you home directory also. Like I said, it doesn't matter as long as you know where it is.